mm: lock a vma before stack expansion

[platform/kernel/linux-rpi.git] / mm / migrate.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Memory Migration functionality - linux/mm/migrate.c
 *
 * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
 *
 * Page migration was first developed in the context of the memory hotplug
 * project. The main authors of the migration code are:
 *
 * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
 * Hirokazu Takahashi <taka@valinux.co.jp>
 * Dave Hansen <haveblue@us.ibm.com>
 * Christoph Lameter
 */

#include <linux/migrate.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/buffer_head.h>
#include <linux/mm_inline.h>
#include <linux/nsproxy.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/topology.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/writeback.h>
#include <linux/mempolicy.h>
#include <linux/vmalloc.h>
#include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/compaction.h>
#include <linux/syscalls.h>
#include <linux/compat.h>
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
#include <linux/gfp.h>
#include <linux/pfn_t.h>
#include <linux/memremap.h>
#include <linux/userfaultfd_k.h>
#include <linux/balloon_compaction.h>
#include <linux/page_idle.h>
#include <linux/page_owner.h>
#include <linux/sched/mm.h>
#include <linux/ptrace.h>
#include <linux/oom.h>
#include <linux/memory.h>
#include <linux/random.h>
#include <linux/sched/sysctl.h>
#include <linux/memory-tiers.h>

#include <asm/tlbflush.h>

#include <trace/events/migrate.h>

#include "internal.h"

bool isolate_movable_page(struct page *page, isolate_mode_t mode)
{
        struct folio *folio = folio_get_nontail_page(page);
        const struct movable_operations *mops;

        /*
         * Avoid burning cycles with pages that are yet under __free_pages(),
         * or just got freed under us.
         *
         * In case we 'win' a race for a movable page being freed under us and
         * raise its refcount preventing __free_pages() from doing its job
         * the put_page() at the end of this block will take care of
         * release this page, thus avoiding a nasty leakage.
         */
        if (!folio)
                goto out;

        if (unlikely(folio_test_slab(folio)))
                goto out_putfolio;
        /* Pairs with smp_wmb() in slab freeing, e.g. SLUB's __free_slab() */
        smp_rmb();
        /*
         * Check movable flag before taking the page lock because
         * we use non-atomic bitops on newly allocated page flags so
         * unconditionally grabbing the lock ruins page's owner side.
         */
        if (unlikely(!__folio_test_movable(folio)))
                goto out_putfolio;
        /* Pairs with smp_wmb() in slab allocation, e.g. SLUB's alloc_slab_page() */
        smp_rmb();
        if (unlikely(folio_test_slab(folio)))
                goto out_putfolio;

        /*
         * As movable pages are not isolated from LRU lists, concurrent
         * compaction threads can race against page migration functions
         * as well as race against the releasing a page.
         *
         * In order to avoid having an already isolated movable page
         * being (wrongly) re-isolated while it is under migration,
         * or to avoid attempting to isolate pages being released,
         * lets be sure we have the page lock
         * before proceeding with the movable page isolation steps.
         */
        if (unlikely(!folio_trylock(folio)))
                goto out_putfolio;

        if (!folio_test_movable(folio) || folio_test_isolated(folio))
                goto out_no_isolated;

        mops = folio_movable_ops(folio);
        VM_BUG_ON_FOLIO(!mops, folio);

        if (!mops->isolate_page(&folio->page, mode))
                goto out_no_isolated;

        /* Driver shouldn't use PG_isolated bit of page->flags */
        WARN_ON_ONCE(folio_test_isolated(folio));
        folio_set_isolated(folio);
        folio_unlock(folio);

        return true;

out_no_isolated:
        folio_unlock(folio);
out_putfolio:
        folio_put(folio);
out:
        return false;
}

static void putback_movable_folio(struct folio *folio)
{
        const struct movable_operations *mops = folio_movable_ops(folio);

        mops->putback_page(&folio->page);
        folio_clear_isolated(folio);
}

/*
 * Put previously isolated pages back onto the appropriate lists
 * from where they were once taken off for compaction/migration.
 *
 * This function shall be used whenever the isolated pageset has been
 * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
 * and isolate_hugetlb().
 */
void putback_movable_pages(struct list_head *l)
{
        struct folio *folio;
        struct folio *folio2;

        list_for_each_entry_safe(folio, folio2, l, lru) {
                if (unlikely(folio_test_hugetlb(folio))) {
                        folio_putback_active_hugetlb(folio);
                        continue;
                }
                list_del(&folio->lru);
                /*
                 * We isolated non-lru movable folio so here we can use
                 * __PageMovable because LRU folio's mapping cannot have
                 * PAGE_MAPPING_MOVABLE.
                 */
                if (unlikely(__folio_test_movable(folio))) {
                        VM_BUG_ON_FOLIO(!folio_test_isolated(folio), folio);
                        folio_lock(folio);
                        if (folio_test_movable(folio))
                                putback_movable_folio(folio);
                        else
                                folio_clear_isolated(folio);
                        folio_unlock(folio);
                        folio_put(folio);
                } else {
                        node_stat_mod_folio(folio, NR_ISOLATED_ANON +
                                        folio_is_file_lru(folio), -folio_nr_pages(folio));
                        folio_putback_lru(folio);
                }
        }
}

/*
 * Restore a potential migration pte to a working pte entry
 */
static bool remove_migration_pte(struct folio *folio,
                struct vm_area_struct *vma, unsigned long addr, void *old)
{
        DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr, PVMW_SYNC | PVMW_MIGRATION);

        while (page_vma_mapped_walk(&pvmw)) {
                rmap_t rmap_flags = RMAP_NONE;
                pte_t old_pte;
                pte_t pte;
                swp_entry_t entry;
                struct page *new;
                unsigned long idx = 0;

                /* pgoff is invalid for ksm pages, but they are never large */
                if (folio_test_large(folio) && !folio_test_hugetlb(folio))
                        idx = linear_page_index(vma, pvmw.address) - pvmw.pgoff;
                new = folio_page(folio, idx);

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
                /* PMD-mapped THP migration entry */
                if (!pvmw.pte) {
                        VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
                                        !folio_test_pmd_mappable(folio), folio);
                        remove_migration_pmd(&pvmw, new);
                        continue;
                }
#endif

                folio_get(folio);
                pte = mk_pte(new, READ_ONCE(vma->vm_page_prot));
                old_pte = ptep_get(pvmw.pte);
                if (pte_swp_soft_dirty(old_pte))
                        pte = pte_mksoft_dirty(pte);

                entry = pte_to_swp_entry(old_pte);
                if (!is_migration_entry_young(entry))
                        pte = pte_mkold(pte);
                if (folio_test_dirty(folio) && is_migration_entry_dirty(entry))
                        pte = pte_mkdirty(pte);
                if (is_writable_migration_entry(entry))
                        pte = pte_mkwrite(pte);
                else if (pte_swp_uffd_wp(old_pte))
                        pte = pte_mkuffd_wp(pte);

                if (folio_test_anon(folio) && !is_readable_migration_entry(entry))
                        rmap_flags |= RMAP_EXCLUSIVE;

                if (unlikely(is_device_private_page(new))) {
                        if (pte_write(pte))
                                entry = make_writable_device_private_entry(
                                                        page_to_pfn(new));
                        else
                                entry = make_readable_device_private_entry(
                                                        page_to_pfn(new));
                        pte = swp_entry_to_pte(entry);
                        if (pte_swp_soft_dirty(old_pte))
                                pte = pte_swp_mksoft_dirty(pte);
                        if (pte_swp_uffd_wp(old_pte))
                                pte = pte_swp_mkuffd_wp(pte);
                }

#ifdef CONFIG_HUGETLB_PAGE
                if (folio_test_hugetlb(folio)) {
                        unsigned int shift = huge_page_shift(hstate_vma(vma));

                        pte = arch_make_huge_pte(pte, shift, vma->vm_flags);
                        if (folio_test_anon(folio))
                                hugepage_add_anon_rmap(new, vma, pvmw.address,
                                                       rmap_flags);
                        else
                                page_dup_file_rmap(new, true);
                        set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
                } else
#endif
                {
                        if (folio_test_anon(folio))
                                page_add_anon_rmap(new, vma, pvmw.address,
                                                   rmap_flags);
                        else
                                page_add_file_rmap(new, vma, false);
                        set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
                }
                if (vma->vm_flags & VM_LOCKED)
                        mlock_drain_local();

                trace_remove_migration_pte(pvmw.address, pte_val(pte),
                                           compound_order(new));

                /* No need to invalidate - it was non-present before */
                update_mmu_cache(vma, pvmw.address, pvmw.pte);
        }

        return true;
}

/*
 * Get rid of all migration entries and replace them by
 * references to the indicated page.
 */
void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked)
{
        struct rmap_walk_control rwc = {
                .rmap_one = remove_migration_pte,
                .arg = src,
        };

        if (locked)
                rmap_walk_locked(dst, &rwc);
        else
                rmap_walk(dst, &rwc);
}

/*
 * Something used the pte of a page under migration. We need to
 * get to the page and wait until migration is finished.
 * When we return from this function the fault will be retried.
 */
void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
                          unsigned long address)
{
        spinlock_t *ptl;
        pte_t *ptep;
        pte_t pte;
        swp_entry_t entry;

        ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
        if (!ptep)
                return;

        pte = ptep_get(ptep);
        pte_unmap(ptep);

        if (!is_swap_pte(pte))
                goto out;

        entry = pte_to_swp_entry(pte);
        if (!is_migration_entry(entry))
                goto out;

        migration_entry_wait_on_locked(entry, ptl);
        return;
out:
        spin_unlock(ptl);
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * The vma read lock must be held upon entry. Holding that lock prevents either
 * the pte or the ptl from being freed.
 *
 * This function will release the vma lock before returning.
 */
void migration_entry_wait_huge(struct vm_area_struct *vma, pte_t *ptep)
{
        spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), vma->vm_mm, ptep);
        pte_t pte;

        hugetlb_vma_assert_locked(vma);
        spin_lock(ptl);
        pte = huge_ptep_get(ptep);

        if (unlikely(!is_hugetlb_entry_migration(pte))) {
                spin_unlock(ptl);
                hugetlb_vma_unlock_read(vma);
        } else {
                /*
                 * If migration entry existed, safe to release vma lock
                 * here because the pgtable page won't be freed without the
                 * pgtable lock released.  See comment right above pgtable
                 * lock release in migration_entry_wait_on_locked().
                 */
                hugetlb_vma_unlock_read(vma);
                migration_entry_wait_on_locked(pte_to_swp_entry(pte), ptl);
        }
}
#endif

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
{
        spinlock_t *ptl;

        ptl = pmd_lock(mm, pmd);
        if (!is_pmd_migration_entry(*pmd))
                goto unlock;
        migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), ptl);
        return;
unlock:
        spin_unlock(ptl);
}
#endif

static int folio_expected_refs(struct address_space *mapping,
                struct folio *folio)
{
        int refs = 1;
        if (!mapping)
                return refs;

        refs += folio_nr_pages(folio);
        if (folio_test_private(folio))
                refs++;

        return refs;
}

/*
 * Replace the page in the mapping.
 *
 * The number of remaining references must be:
 * 1 for anonymous pages without a mapping
 * 2 for pages with a mapping
 * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
 */
int folio_migrate_mapping(struct address_space *mapping,
                struct folio *newfolio, struct folio *folio, int extra_count)
{
        XA_STATE(xas, &mapping->i_pages, folio_index(folio));
        struct zone *oldzone, *newzone;
        int dirty;
        int expected_count = folio_expected_refs(mapping, folio) + extra_count;
        long nr = folio_nr_pages(folio);

        if (!mapping) {
                /* Anonymous page without mapping */
                if (folio_ref_count(folio) != expected_count)
                        return -EAGAIN;

                /* No turning back from here */
                newfolio->index = folio->index;
                newfolio->mapping = folio->mapping;
                if (folio_test_swapbacked(folio))
                        __folio_set_swapbacked(newfolio);

                return MIGRATEPAGE_SUCCESS;
        }

        oldzone = folio_zone(folio);
        newzone = folio_zone(newfolio);

        xas_lock_irq(&xas);
        if (!folio_ref_freeze(folio, expected_count)) {
                xas_unlock_irq(&xas);
                return -EAGAIN;
        }

        /*
         * Now we know that no one else is looking at the folio:
         * no turning back from here.
         */
        newfolio->index = folio->index;
        newfolio->mapping = folio->mapping;
        folio_ref_add(newfolio, nr); /* add cache reference */
        if (folio_test_swapbacked(folio)) {
                __folio_set_swapbacked(newfolio);
                if (folio_test_swapcache(folio)) {
                        folio_set_swapcache(newfolio);
                        newfolio->private = folio_get_private(folio);
                }
        } else {
                VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
        }

        /* Move dirty while page refs frozen and newpage not yet exposed */
        dirty = folio_test_dirty(folio);
        if (dirty) {
                folio_clear_dirty(folio);
                folio_set_dirty(newfolio);
        }

        xas_store(&xas, newfolio);

        /*
         * Drop cache reference from old page by unfreezing
         * to one less reference.
         * We know this isn't the last reference.
         */
        folio_ref_unfreeze(folio, expected_count - nr);

        xas_unlock(&xas);
        /* Leave irq disabled to prevent preemption while updating stats */

        /*
         * If moved to a different zone then also account
         * the page for that zone. Other VM counters will be
         * taken care of when we establish references to the
         * new page and drop references to the old page.
         *
         * Note that anonymous pages are accounted for
         * via NR_FILE_PAGES and NR_ANON_MAPPED if they
         * are mapped to swap space.
         */
        if (newzone != oldzone) {
                struct lruvec *old_lruvec, *new_lruvec;
                struct mem_cgroup *memcg;

                memcg = folio_memcg(folio);
                old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat);
                new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat);

                __mod_lruvec_state(old_lruvec, NR_FILE_PAGES, -nr);
                __mod_lruvec_state(new_lruvec, NR_FILE_PAGES, nr);
                if (folio_test_swapbacked(folio) && !folio_test_swapcache(folio)) {
                        __mod_lruvec_state(old_lruvec, NR_SHMEM, -nr);
                        __mod_lruvec_state(new_lruvec, NR_SHMEM, nr);

                        if (folio_test_pmd_mappable(folio)) {
                                __mod_lruvec_state(old_lruvec, NR_SHMEM_THPS, -nr);
                                __mod_lruvec_state(new_lruvec, NR_SHMEM_THPS, nr);
                        }
                }
#ifdef CONFIG_SWAP
                if (folio_test_swapcache(folio)) {
                        __mod_lruvec_state(old_lruvec, NR_SWAPCACHE, -nr);
                        __mod_lruvec_state(new_lruvec, NR_SWAPCACHE, nr);
                }
#endif
                if (dirty && mapping_can_writeback(mapping)) {
                        __mod_lruvec_state(old_lruvec, NR_FILE_DIRTY, -nr);
                        __mod_zone_page_state(oldzone, NR_ZONE_WRITE_PENDING, -nr);
                        __mod_lruvec_state(new_lruvec, NR_FILE_DIRTY, nr);
                        __mod_zone_page_state(newzone, NR_ZONE_WRITE_PENDING, nr);
                }
        }
        local_irq_enable();

        return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL(folio_migrate_mapping);

/*
 * The expected number of remaining references is the same as that
 * of folio_migrate_mapping().
 */
int migrate_huge_page_move_mapping(struct address_space *mapping,
                                   struct folio *dst, struct folio *src)
{
        XA_STATE(xas, &mapping->i_pages, folio_index(src));
        int expected_count;

        xas_lock_irq(&xas);
        expected_count = 2 + folio_has_private(src);
        if (!folio_ref_freeze(src, expected_count)) {
                xas_unlock_irq(&xas);
                return -EAGAIN;
        }

        dst->index = src->index;
        dst->mapping = src->mapping;

        folio_get(dst);

        xas_store(&xas, dst);

        folio_ref_unfreeze(src, expected_count - 1);

        xas_unlock_irq(&xas);

        return MIGRATEPAGE_SUCCESS;
}

/*
 * Copy the flags and some other ancillary information
 */
void folio_migrate_flags(struct folio *newfolio, struct folio *folio)
{
        int cpupid;

        if (folio_test_error(folio))
                folio_set_error(newfolio);
        if (folio_test_referenced(folio))
                folio_set_referenced(newfolio);
        if (folio_test_uptodate(folio))
                folio_mark_uptodate(newfolio);
        if (folio_test_clear_active(folio)) {
                VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio);
                folio_set_active(newfolio);
        } else if (folio_test_clear_unevictable(folio))
                folio_set_unevictable(newfolio);
        if (folio_test_workingset(folio))
                folio_set_workingset(newfolio);
        if (folio_test_checked(folio))
                folio_set_checked(newfolio);
        /*
         * PG_anon_exclusive (-> PG_mappedtodisk) is always migrated via
         * migration entries. We can still have PG_anon_exclusive set on an
         * effectively unmapped and unreferenced first sub-pages of an
         * anonymous THP: we can simply copy it here via PG_mappedtodisk.
         */
        if (folio_test_mappedtodisk(folio))
                folio_set_mappedtodisk(newfolio);

        /* Move dirty on pages not done by folio_migrate_mapping() */
        if (folio_test_dirty(folio))
                folio_set_dirty(newfolio);

        if (folio_test_young(folio))
                folio_set_young(newfolio);
        if (folio_test_idle(folio))
                folio_set_idle(newfolio);

        /*
         * Copy NUMA information to the new page, to prevent over-eager
         * future migrations of this same page.
         */
        cpupid = page_cpupid_xchg_last(&folio->page, -1);
        /*
         * For memory tiering mode, when migrate between slow and fast
         * memory node, reset cpupid, because that is used to record
         * page access time in slow memory node.
         */
        if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) {
                bool f_toptier = node_is_toptier(page_to_nid(&folio->page));
                bool t_toptier = node_is_toptier(page_to_nid(&newfolio->page));

                if (f_toptier != t_toptier)
                        cpupid = -1;
        }
        page_cpupid_xchg_last(&newfolio->page, cpupid);

        folio_migrate_ksm(newfolio, folio);
        /*
         * Please do not reorder this without considering how mm/ksm.c's
         * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
         */
        if (folio_test_swapcache(folio))
                folio_clear_swapcache(folio);
        folio_clear_private(folio);

        /* page->private contains hugetlb specific flags */
        if (!folio_test_hugetlb(folio))
                folio->private = NULL;

        /*
         * If any waiters have accumulated on the new page then
         * wake them up.
         */
        if (folio_test_writeback(newfolio))
                folio_end_writeback(newfolio);

        /*
         * PG_readahead shares the same bit with PG_reclaim.  The above
         * end_page_writeback() may clear PG_readahead mistakenly, so set the
         * bit after that.
         */
        if (folio_test_readahead(folio))
                folio_set_readahead(newfolio);

        folio_copy_owner(newfolio, folio);

        if (!folio_test_hugetlb(folio))
                mem_cgroup_migrate(folio, newfolio);
}
EXPORT_SYMBOL(folio_migrate_flags);

void folio_migrate_copy(struct folio *newfolio, struct folio *folio)
{
        folio_copy(newfolio, folio);
        folio_migrate_flags(newfolio, folio);
}
EXPORT_SYMBOL(folio_migrate_copy);

/************************************************************
 *                    Migration functions
 ***********************************************************/

int migrate_folio_extra(struct address_space *mapping, struct folio *dst,
                struct folio *src, enum migrate_mode mode, int extra_count)
{
        int rc;

        BUG_ON(folio_test_writeback(src));      /* Writeback must be complete */

        rc = folio_migrate_mapping(mapping, dst, src, extra_count);

        if (rc != MIGRATEPAGE_SUCCESS)
                return rc;

        if (mode != MIGRATE_SYNC_NO_COPY)
                folio_migrate_copy(dst, src);
        else
                folio_migrate_flags(dst, src);
        return MIGRATEPAGE_SUCCESS;
}

/**
 * migrate_folio() - Simple folio migration.
 * @mapping: The address_space containing the folio.
 * @dst: The folio to migrate the data to.
 * @src: The folio containing the current data.
 * @mode: How to migrate the page.
 *
 * Common logic to directly migrate a single LRU folio suitable for
 * folios that do not use PagePrivate/PagePrivate2.
 *
 * Folios are locked upon entry and exit.
 */
int migrate_folio(struct address_space *mapping, struct folio *dst,
                struct folio *src, enum migrate_mode mode)
{
        return migrate_folio_extra(mapping, dst, src, mode, 0);
}
EXPORT_SYMBOL(migrate_folio);

#ifdef CONFIG_BLOCK
/* Returns true if all buffers are successfully locked */
static bool buffer_migrate_lock_buffers(struct buffer_head *head,
                                                        enum migrate_mode mode)
{
        struct buffer_head *bh = head;
        struct buffer_head *failed_bh;

        do {
                if (!trylock_buffer(bh)) {
                        if (mode == MIGRATE_ASYNC)
                                goto unlock;
                        if (mode == MIGRATE_SYNC_LIGHT && !buffer_uptodate(bh))
                                goto unlock;
                        lock_buffer(bh);
                }

                bh = bh->b_this_page;
        } while (bh != head);

        return true;

unlock:
        /* We failed to lock the buffer and cannot stall. */
        failed_bh = bh;
        bh = head;
        while (bh != failed_bh) {
                unlock_buffer(bh);
                bh = bh->b_this_page;
        }

        return false;
}

static int __buffer_migrate_folio(struct address_space *mapping,
                struct folio *dst, struct folio *src, enum migrate_mode mode,
                bool check_refs)
{
        struct buffer_head *bh, *head;
        int rc;
        int expected_count;

        head = folio_buffers(src);
        if (!head)
                return migrate_folio(mapping, dst, src, mode);

        /* Check whether page does not have extra refs before we do more work */
        expected_count = folio_expected_refs(mapping, src);
        if (folio_ref_count(src) != expected_count)
                return -EAGAIN;

        if (!buffer_migrate_lock_buffers(head, mode))
                return -EAGAIN;

        if (check_refs) {
                bool busy;
                bool invalidated = false;

recheck_buffers:
                busy = false;
                spin_lock(&mapping->private_lock);
                bh = head;
                do {
                        if (atomic_read(&bh->b_count)) {
                                busy = true;
                                break;
                        }
                        bh = bh->b_this_page;
                } while (bh != head);
                if (busy) {
                        if (invalidated) {
                                rc = -EAGAIN;
                                goto unlock_buffers;
                        }
                        spin_unlock(&mapping->private_lock);
                        invalidate_bh_lrus();
                        invalidated = true;
                        goto recheck_buffers;
                }
        }

        rc = folio_migrate_mapping(mapping, dst, src, 0);
        if (rc != MIGRATEPAGE_SUCCESS)
                goto unlock_buffers;

        folio_attach_private(dst, folio_detach_private(src));

        bh = head;
        do {
                set_bh_page(bh, &dst->page, bh_offset(bh));
                bh = bh->b_this_page;
        } while (bh != head);

        if (mode != MIGRATE_SYNC_NO_COPY)
                folio_migrate_copy(dst, src);
        else
                folio_migrate_flags(dst, src);

        rc = MIGRATEPAGE_SUCCESS;
unlock_buffers:
        if (check_refs)
                spin_unlock(&mapping->private_lock);
        bh = head;
        do {
                unlock_buffer(bh);
                bh = bh->b_this_page;
        } while (bh != head);

        return rc;
}

/**
 * buffer_migrate_folio() - Migration function for folios with buffers.
 * @mapping: The address space containing @src.
 * @dst: The folio to migrate to.
 * @src: The folio to migrate from.
 * @mode: How to migrate the folio.
 *
 * This function can only be used if the underlying filesystem guarantees
 * that no other references to @src exist. For example attached buffer
 * heads are accessed only under the folio lock.  If your filesystem cannot
 * provide this guarantee, buffer_migrate_folio_norefs() may be more
 * appropriate.
 *
 * Return: 0 on success or a negative errno on failure.
 */
int buffer_migrate_folio(struct address_space *mapping,
                struct folio *dst, struct folio *src, enum migrate_mode mode)
{
        return __buffer_migrate_folio(mapping, dst, src, mode, false);
}
EXPORT_SYMBOL(buffer_migrate_folio);

/**
 * buffer_migrate_folio_norefs() - Migration function for folios with buffers.
 * @mapping: The address space containing @src.
 * @dst: The folio to migrate to.
 * @src: The folio to migrate from.
 * @mode: How to migrate the folio.
 *
 * Like buffer_migrate_folio() except that this variant is more careful
 * and checks that there are also no buffer head references. This function
 * is the right one for mappings where buffer heads are directly looked
 * up and referenced (such as block device mappings).
 *
 * Return: 0 on success or a negative errno on failure.
 */
int buffer_migrate_folio_norefs(struct address_space *mapping,
                struct folio *dst, struct folio *src, enum migrate_mode mode)
{
        return __buffer_migrate_folio(mapping, dst, src, mode, true);
}
EXPORT_SYMBOL_GPL(buffer_migrate_folio_norefs);
#endif

int filemap_migrate_folio(struct address_space *mapping,
                struct folio *dst, struct folio *src, enum migrate_mode mode)
{
        int ret;

        ret = folio_migrate_mapping(mapping, dst, src, 0);
        if (ret != MIGRATEPAGE_SUCCESS)
                return ret;

        if (folio_get_private(src))
                folio_attach_private(dst, folio_detach_private(src));

        if (mode != MIGRATE_SYNC_NO_COPY)
                folio_migrate_copy(dst, src);
        else
                folio_migrate_flags(dst, src);
        return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL_GPL(filemap_migrate_folio);

/*
 * Writeback a folio to clean the dirty state
 */
static int writeout(struct address_space *mapping, struct folio *folio)
{
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_NONE,
                .nr_to_write = 1,
                .range_start = 0,
                .range_end = LLONG_MAX,
                .for_reclaim = 1
        };
        int rc;

        if (!mapping->a_ops->writepage)
                /* No write method for the address space */
                return -EINVAL;

        if (!folio_clear_dirty_for_io(folio))
                /* Someone else already triggered a write */
                return -EAGAIN;

        /*
         * A dirty folio may imply that the underlying filesystem has
         * the folio on some queue. So the folio must be clean for
         * migration. Writeout may mean we lose the lock and the
         * folio state is no longer what we checked for earlier.
         * At this point we know that the migration attempt cannot
         * be successful.
         */
        remove_migration_ptes(folio, folio, false);

        rc = mapping->a_ops->writepage(&folio->page, &wbc);

        if (rc != AOP_WRITEPAGE_ACTIVATE)
                /* unlocked. Relock */
                folio_lock(folio);

        return (rc < 0) ? -EIO : -EAGAIN;
}

/*
 * Default handling if a filesystem does not provide a migration function.
 */
static int fallback_migrate_folio(struct address_space *mapping,
                struct folio *dst, struct folio *src, enum migrate_mode mode)
{
        if (folio_test_dirty(src)) {
                /* Only writeback folios in full synchronous migration */
                switch (mode) {
                case MIGRATE_SYNC:
                case MIGRATE_SYNC_NO_COPY:
                        break;
                default:
                        return -EBUSY;
                }
                return writeout(mapping, src);
        }

        /*
         * Buffers may be managed in a filesystem specific way.
         * We must have no buffers or drop them.
         */
        if (folio_test_private(src) &&
            !filemap_release_folio(src, GFP_KERNEL))
                return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY;

        return migrate_folio(mapping, dst, src, mode);
}

/*
 * Move a page to a newly allocated page
 * The page is locked and all ptes have been successfully removed.
 *
 * The new page will have replaced the old page if this function
 * is successful.
 *
 * Return value:
 *   < 0 - error code
 *  MIGRATEPAGE_SUCCESS - success
 */
static int move_to_new_folio(struct folio *dst, struct folio *src,
                                enum migrate_mode mode)
{
        int rc = -EAGAIN;
        bool is_lru = !__PageMovable(&src->page);

        VM_BUG_ON_FOLIO(!folio_test_locked(src), src);
        VM_BUG_ON_FOLIO(!folio_test_locked(dst), dst);

        if (likely(is_lru)) {
                struct address_space *mapping = folio_mapping(src);

                if (!mapping)
                        rc = migrate_folio(mapping, dst, src, mode);
                else if (mapping->a_ops->migrate_folio)
                        /*
                         * Most folios have a mapping and most filesystems
                         * provide a migrate_folio callback. Anonymous folios
                         * are part of swap space which also has its own
                         * migrate_folio callback. This is the most common path
                         * for page migration.
                         */
                        rc = mapping->a_ops->migrate_folio(mapping, dst, src,
                                                                mode);
                else
                        rc = fallback_migrate_folio(mapping, dst, src, mode);
        } else {
                const struct movable_operations *mops;

                /*
                 * In case of non-lru page, it could be released after
                 * isolation step. In that case, we shouldn't try migration.
                 */
                VM_BUG_ON_FOLIO(!folio_test_isolated(src), src);
                if (!folio_test_movable(src)) {
                        rc = MIGRATEPAGE_SUCCESS;
                        folio_clear_isolated(src);
                        goto out;
                }

                mops = folio_movable_ops(src);
                rc = mops->migrate_page(&dst->page, &src->page, mode);
                WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
                                !folio_test_isolated(src));
        }

        /*
         * When successful, old pagecache src->mapping must be cleared before
         * src is freed; but stats require that PageAnon be left as PageAnon.
         */
        if (rc == MIGRATEPAGE_SUCCESS) {
                if (__PageMovable(&src->page)) {
                        VM_BUG_ON_FOLIO(!folio_test_isolated(src), src);

                        /*
                         * We clear PG_movable under page_lock so any compactor
                         * cannot try to migrate this page.
                         */
                        folio_clear_isolated(src);
                }

                /*
                 * Anonymous and movable src->mapping will be cleared by
                 * free_pages_prepare so don't reset it here for keeping
                 * the type to work PageAnon, for example.
                 */
                if (!folio_mapping_flags(src))
                        src->mapping = NULL;

                if (likely(!folio_is_zone_device(dst)))
                        flush_dcache_folio(dst);
        }
out:
        return rc;
}

/*
 * To record some information during migration, we use some unused
 * fields (mapping and private) of struct folio of the newly allocated
 * destination folio.  This is safe because nobody is using them
 * except us.
 */
union migration_ptr {
        struct anon_vma *anon_vma;
        struct address_space *mapping;
};
static void __migrate_folio_record(struct folio *dst,
                                   unsigned long page_was_mapped,
                                   struct anon_vma *anon_vma)
{
        union migration_ptr ptr = { .anon_vma = anon_vma };
        dst->mapping = ptr.mapping;
        dst->private = (void *)page_was_mapped;
}

static void __migrate_folio_extract(struct folio *dst,
                                   int *page_was_mappedp,
                                   struct anon_vma **anon_vmap)
{
        union migration_ptr ptr = { .mapping = dst->mapping };
        *anon_vmap = ptr.anon_vma;
        *page_was_mappedp = (unsigned long)dst->private;
        dst->mapping = NULL;
        dst->private = NULL;
}

/* Restore the source folio to the original state upon failure */
static void migrate_folio_undo_src(struct folio *src,
                                   int page_was_mapped,
                                   struct anon_vma *anon_vma,
                                   bool locked,
                                   struct list_head *ret)
{
        if (page_was_mapped)
                remove_migration_ptes(src, src, false);
        /* Drop an anon_vma reference if we took one */
        if (anon_vma)
                put_anon_vma(anon_vma);
        if (locked)
                folio_unlock(src);
        if (ret)
                list_move_tail(&src->lru, ret);
}

/* Restore the destination folio to the original state upon failure */
static void migrate_folio_undo_dst(struct folio *dst, bool locked,
                free_folio_t put_new_folio, unsigned long private)
{
        if (locked)
                folio_unlock(dst);
        if (put_new_folio)
                put_new_folio(dst, private);
        else
                folio_put(dst);
}

/* Cleanup src folio upon migration success */
static void migrate_folio_done(struct folio *src,
                               enum migrate_reason reason)
{
        /*
         * Compaction can migrate also non-LRU pages which are
         * not accounted to NR_ISOLATED_*. They can be recognized
         * as __PageMovable
         */
        if (likely(!__folio_test_movable(src)))
                mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
                                    folio_is_file_lru(src), -folio_nr_pages(src));

        if (reason != MR_MEMORY_FAILURE)
                /* We release the page in page_handle_poison. */
                folio_put(src);
}

/* Obtain the lock on page, remove all ptes. */
static int migrate_folio_unmap(new_folio_t get_new_folio,
                free_folio_t put_new_folio, unsigned long private,
                struct folio *src, struct folio **dstp, enum migrate_mode mode,
                enum migrate_reason reason, struct list_head *ret)
{
        struct folio *dst;
        int rc = -EAGAIN;
        int page_was_mapped = 0;
        struct anon_vma *anon_vma = NULL;
        bool is_lru = !__PageMovable(&src->page);
        bool locked = false;
        bool dst_locked = false;

        if (folio_ref_count(src) == 1) {
                /* Folio was freed from under us. So we are done. */
                folio_clear_active(src);
                folio_clear_unevictable(src);
                /* free_pages_prepare() will clear PG_isolated. */
                list_del(&src->lru);
                migrate_folio_done(src, reason);
                return MIGRATEPAGE_SUCCESS;
        }

        dst = get_new_folio(src, private);
        if (!dst)
                return -ENOMEM;
        *dstp = dst;

        dst->private = NULL;

        if (!folio_trylock(src)) {
                if (mode == MIGRATE_ASYNC)
                        goto out;

                /*
                 * It's not safe for direct compaction to call lock_page.
                 * For example, during page readahead pages are added locked
                 * to the LRU. Later, when the IO completes the pages are
                 * marked uptodate and unlocked. However, the queueing
                 * could be merging multiple pages for one bio (e.g.
                 * mpage_readahead). If an allocation happens for the
                 * second or third page, the process can end up locking
                 * the same page twice and deadlocking. Rather than
                 * trying to be clever about what pages can be locked,
                 * avoid the use of lock_page for direct compaction
                 * altogether.
                 */
                if (current->flags & PF_MEMALLOC)
                        goto out;

                /*
                 * In "light" mode, we can wait for transient locks (eg
                 * inserting a page into the page table), but it's not
                 * worth waiting for I/O.
                 */
                if (mode == MIGRATE_SYNC_LIGHT && !folio_test_uptodate(src))
                        goto out;

                folio_lock(src);
        }
        locked = true;

        if (folio_test_writeback(src)) {
                /*
                 * Only in the case of a full synchronous migration is it
                 * necessary to wait for PageWriteback. In the async case,
                 * the retry loop is too short and in the sync-light case,
                 * the overhead of stalling is too much
                 */
                switch (mode) {
                case MIGRATE_SYNC:
                case MIGRATE_SYNC_NO_COPY:
                        break;
                default:
                        rc = -EBUSY;
                        goto out;
                }
                folio_wait_writeback(src);
        }

        /*
         * By try_to_migrate(), src->mapcount goes down to 0 here. In this case,
         * we cannot notice that anon_vma is freed while we migrate a page.
         * This get_anon_vma() delays freeing anon_vma pointer until the end
         * of migration. File cache pages are no problem because of page_lock()
         * File Caches may use write_page() or lock_page() in migration, then,
         * just care Anon page here.
         *
         * Only folio_get_anon_vma() understands the subtleties of
         * getting a hold on an anon_vma from outside one of its mms.
         * But if we cannot get anon_vma, then we won't need it anyway,
         * because that implies that the anon page is no longer mapped
         * (and cannot be remapped so long as we hold the page lock).
         */
        if (folio_test_anon(src) && !folio_test_ksm(src))
                anon_vma = folio_get_anon_vma(src);

        /*
         * Block others from accessing the new page when we get around to
         * establishing additional references. We are usually the only one
         * holding a reference to dst at this point. We used to have a BUG
         * here if folio_trylock(dst) fails, but would like to allow for
         * cases where there might be a race with the previous use of dst.
         * This is much like races on refcount of oldpage: just don't BUG().
         */
        if (unlikely(!folio_trylock(dst)))
                goto out;
        dst_locked = true;

        if (unlikely(!is_lru)) {
                __migrate_folio_record(dst, page_was_mapped, anon_vma);
                return MIGRATEPAGE_UNMAP;
        }

        /*
         * Corner case handling:
         * 1. When a new swap-cache page is read into, it is added to the LRU
         * and treated as swapcache but it has no rmap yet.
         * Calling try_to_unmap() against a src->mapping==NULL page will
         * trigger a BUG.  So handle it here.
         * 2. An orphaned page (see truncate_cleanup_page) might have
         * fs-private metadata. The page can be picked up due to memory
         * offlining.  Everywhere else except page reclaim, the page is
         * invisible to the vm, so the page can not be migrated.  So try to
         * free the metadata, so the page can be freed.
         */
        if (!src->mapping) {
                if (folio_test_private(src)) {
                        try_to_free_buffers(src);
                        goto out;
                }
        } else if (folio_mapped(src)) {
                /* Establish migration ptes */
                VM_BUG_ON_FOLIO(folio_test_anon(src) &&
                               !folio_test_ksm(src) && !anon_vma, src);
                try_to_migrate(src, mode == MIGRATE_ASYNC ? TTU_BATCH_FLUSH : 0);
                page_was_mapped = 1;
        }

        if (!folio_mapped(src)) {
                __migrate_folio_record(dst, page_was_mapped, anon_vma);
                return MIGRATEPAGE_UNMAP;
        }

out:
        /*
         * A folio that has not been unmapped will be restored to
         * right list unless we want to retry.
         */
        if (rc == -EAGAIN)
                ret = NULL;

        migrate_folio_undo_src(src, page_was_mapped, anon_vma, locked, ret);
        migrate_folio_undo_dst(dst, dst_locked, put_new_folio, private);

        return rc;
}

/* Migrate the folio to the newly allocated folio in dst. */
static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private,
                              struct folio *src, struct folio *dst,
                              enum migrate_mode mode, enum migrate_reason reason,
                              struct list_head *ret)
{
        int rc;
        int page_was_mapped = 0;
        struct anon_vma *anon_vma = NULL;
        bool is_lru = !__PageMovable(&src->page);
        struct list_head *prev;

        __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
        prev = dst->lru.prev;
        list_del(&dst->lru);

        rc = move_to_new_folio(dst, src, mode);
        if (rc)
                goto out;

        if (unlikely(!is_lru))
                goto out_unlock_both;

        /*
         * When successful, push dst to LRU immediately: so that if it
         * turns out to be an mlocked page, remove_migration_ptes() will
         * automatically build up the correct dst->mlock_count for it.
         *
         * We would like to do something similar for the old page, when
         * unsuccessful, and other cases when a page has been temporarily
         * isolated from the unevictable LRU: but this case is the easiest.
         */
        folio_add_lru(dst);
        if (page_was_mapped)
                lru_add_drain();

        if (page_was_mapped)
                remove_migration_ptes(src, dst, false);

out_unlock_both:
        folio_unlock(dst);
        set_page_owner_migrate_reason(&dst->page, reason);
        /*
         * If migration is successful, decrease refcount of dst,
         * which will not free the page because new page owner increased
         * refcounter.
         */
        folio_put(dst);

        /*
         * A folio that has been migrated has all references removed
         * and will be freed.
         */
        list_del(&src->lru);
        /* Drop an anon_vma reference if we took one */
        if (anon_vma)
                put_anon_vma(anon_vma);
        folio_unlock(src);
        migrate_folio_done(src, reason);

        return rc;
out:
        /*
         * A folio that has not been migrated will be restored to
         * right list unless we want to retry.
         */
        if (rc == -EAGAIN) {
                list_add(&dst->lru, prev);
                __migrate_folio_record(dst, page_was_mapped, anon_vma);
                return rc;
        }

        migrate_folio_undo_src(src, page_was_mapped, anon_vma, true, ret);
        migrate_folio_undo_dst(dst, true, put_new_folio, private);

        return rc;
}

/*
 * Counterpart of unmap_and_move_page() for hugepage migration.
 *
 * This function doesn't wait the completion of hugepage I/O
 * because there is no race between I/O and migration for hugepage.
 * Note that currently hugepage I/O occurs only in direct I/O
 * where no lock is held and PG_writeback is irrelevant,
 * and writeback status of all subpages are counted in the reference
 * count of the head page (i.e. if all subpages of a 2MB hugepage are
 * under direct I/O, the reference of the head page is 512 and a bit more.)
 * This means that when we try to migrate hugepage whose subpages are
 * doing direct I/O, some references remain after try_to_unmap() and
 * hugepage migration fails without data corruption.
 *
 * There is also no race when direct I/O is issued on the page under migration,
 * because then pte is replaced with migration swap entry and direct I/O code
 * will wait in the page fault for migration to complete.
 */
static int unmap_and_move_huge_page(new_folio_t get_new_folio,
                free_folio_t put_new_folio, unsigned long private,
                struct folio *src, int force, enum migrate_mode mode,
                int reason, struct list_head *ret)
{
        struct folio *dst;
        int rc = -EAGAIN;
        int page_was_mapped = 0;
        struct anon_vma *anon_vma = NULL;
        struct address_space *mapping = NULL;

        if (folio_ref_count(src) == 1) {
                /* page was freed from under us. So we are done. */
                folio_putback_active_hugetlb(src);
                return MIGRATEPAGE_SUCCESS;
        }

        dst = get_new_folio(src, private);
        if (!dst)
                return -ENOMEM;

        if (!folio_trylock(src)) {
                if (!force)
                        goto out;
                switch (mode) {
                case MIGRATE_SYNC:
                case MIGRATE_SYNC_NO_COPY:
                        break;
                default:
                        goto out;
                }
                folio_lock(src);
        }

        /*
         * Check for pages which are in the process of being freed.  Without
         * folio_mapping() set, hugetlbfs specific move page routine will not
         * be called and we could leak usage counts for subpools.
         */
        if (hugetlb_folio_subpool(src) && !folio_mapping(src)) {
                rc = -EBUSY;
                goto out_unlock;
        }

        if (folio_test_anon(src))
                anon_vma = folio_get_anon_vma(src);

        if (unlikely(!folio_trylock(dst)))
                goto put_anon;

        if (folio_mapped(src)) {
                enum ttu_flags ttu = 0;

                if (!folio_test_anon(src)) {
                        /*
                         * In shared mappings, try_to_unmap could potentially
                         * call huge_pmd_unshare.  Because of this, take
                         * semaphore in write mode here and set TTU_RMAP_LOCKED
                         * to let lower levels know we have taken the lock.
                         */
                        mapping = hugetlb_page_mapping_lock_write(&src->page);
                        if (unlikely(!mapping))
                                goto unlock_put_anon;

                        ttu = TTU_RMAP_LOCKED;
                }

                try_to_migrate(src, ttu);
                page_was_mapped = 1;

                if (ttu & TTU_RMAP_LOCKED)
                        i_mmap_unlock_write(mapping);
        }

        if (!folio_mapped(src))
                rc = move_to_new_folio(dst, src, mode);

        if (page_was_mapped)
                remove_migration_ptes(src,
                        rc == MIGRATEPAGE_SUCCESS ? dst : src, false);

unlock_put_anon:
        folio_unlock(dst);

put_anon:
        if (anon_vma)
                put_anon_vma(anon_vma);

        if (rc == MIGRATEPAGE_SUCCESS) {
                move_hugetlb_state(src, dst, reason);
                put_new_folio = NULL;
        }

out_unlock:
        folio_unlock(src);
out:
        if (rc == MIGRATEPAGE_SUCCESS)
                folio_putback_active_hugetlb(src);
        else if (rc != -EAGAIN)
                list_move_tail(&src->lru, ret);

        /*
         * If migration was not successful and there's a freeing callback, use
         * it.  Otherwise, put_page() will drop the reference grabbed during
         * isolation.
         */
        if (put_new_folio)
                put_new_folio(dst, private);
        else
                folio_putback_active_hugetlb(dst);

        return rc;
}

static inline int try_split_folio(struct folio *folio, struct list_head *split_folios)
{
        int rc;

        folio_lock(folio);
        rc = split_folio_to_list(folio, split_folios);
        folio_unlock(folio);
        if (!rc)
                list_move_tail(&folio->lru, split_folios);

        return rc;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define NR_MAX_BATCHED_MIGRATION        HPAGE_PMD_NR
#else
#define NR_MAX_BATCHED_MIGRATION        512
#endif
#define NR_MAX_MIGRATE_PAGES_RETRY      10
#define NR_MAX_MIGRATE_ASYNC_RETRY      3
#define NR_MAX_MIGRATE_SYNC_RETRY                                       \
        (NR_MAX_MIGRATE_PAGES_RETRY - NR_MAX_MIGRATE_ASYNC_RETRY)

struct migrate_pages_stats {
        int nr_succeeded;       /* Normal and large folios migrated successfully, in
                                   units of base pages */
        int nr_failed_pages;    /* Normal and large folios failed to be migrated, in
                                   units of base pages.  Untried folios aren't counted */
        int nr_thp_succeeded;   /* THP migrated successfully */
        int nr_thp_failed;      /* THP failed to be migrated */
        int nr_thp_split;       /* THP split before migrating */
};

/*
 * Returns the number of hugetlb folios that were not migrated, or an error code
 * after NR_MAX_MIGRATE_PAGES_RETRY attempts or if no hugetlb folios are movable
 * any more because the list has become empty or no retryable hugetlb folios
 * exist any more. It is caller's responsibility to call putback_movable_pages()
 * only if ret != 0.
 */
static int migrate_hugetlbs(struct list_head *from, new_folio_t get_new_folio,
                            free_folio_t put_new_folio, unsigned long private,
                            enum migrate_mode mode, int reason,
                            struct migrate_pages_stats *stats,
                            struct list_head *ret_folios)
{
        int retry = 1;
        int nr_failed = 0;
        int nr_retry_pages = 0;
        int pass = 0;
        struct folio *folio, *folio2;
        int rc, nr_pages;

        for (pass = 0; pass < NR_MAX_MIGRATE_PAGES_RETRY && retry; pass++) {
                retry = 0;
                nr_retry_pages = 0;

                list_for_each_entry_safe(folio, folio2, from, lru) {
                        if (!folio_test_hugetlb(folio))
                                continue;

                        nr_pages = folio_nr_pages(folio);

                        cond_resched();

                        /*
                         * Migratability of hugepages depends on architectures and
                         * their size.  This check is necessary because some callers
                         * of hugepage migration like soft offline and memory
                         * hotremove don't walk through page tables or check whether
                         * the hugepage is pmd-based or not before kicking migration.
                         */
                        if (!hugepage_migration_supported(folio_hstate(folio))) {
                                nr_failed++;
                                stats->nr_failed_pages += nr_pages;
                                list_move_tail(&folio->lru, ret_folios);
                                continue;
                        }

                        rc = unmap_and_move_huge_page(get_new_folio,
                                                      put_new_folio, private,
                                                      folio, pass > 2, mode,
                                                      reason, ret_folios);
                        /*
                         * The rules are:
                         *      Success: hugetlb folio will be put back
                         *      -EAGAIN: stay on the from list
                         *      -ENOMEM: stay on the from list
                         *      Other errno: put on ret_folios list
                         */
                        switch(rc) {
                        case -ENOMEM:
                                /*
                                 * When memory is low, don't bother to try to migrate
                                 * other folios, just exit.
                                 */
                                stats->nr_failed_pages += nr_pages + nr_retry_pages;
                                return -ENOMEM;
                        case -EAGAIN:
                                retry++;
                                nr_retry_pages += nr_pages;
                                break;
                        case MIGRATEPAGE_SUCCESS:
                                stats->nr_succeeded += nr_pages;
                                break;
                        default:
                                /*
                                 * Permanent failure (-EBUSY, etc.):
                                 * unlike -EAGAIN case, the failed folio is
                                 * removed from migration folio list and not
                                 * retried in the next outer loop.
                                 */
                                nr_failed++;
                                stats->nr_failed_pages += nr_pages;
                                break;
                        }
                }
        }
        /*
         * nr_failed is number of hugetlb folios failed to be migrated.  After
         * NR_MAX_MIGRATE_PAGES_RETRY attempts, give up and count retried hugetlb
         * folios as failed.
         */
        nr_failed += retry;
        stats->nr_failed_pages += nr_retry_pages;

        return nr_failed;
}

/*
 * migrate_pages_batch() first unmaps folios in the from list as many as
 * possible, then move the unmapped folios.
 *
 * We only batch migration if mode == MIGRATE_ASYNC to avoid to wait a
 * lock or bit when we have locked more than one folio.  Which may cause
 * deadlock (e.g., for loop device).  So, if mode != MIGRATE_ASYNC, the
 * length of the from list must be <= 1.
 */
static int migrate_pages_batch(struct list_head *from,
                new_folio_t get_new_folio, free_folio_t put_new_folio,
                unsigned long private, enum migrate_mode mode, int reason,
                struct list_head *ret_folios, struct list_head *split_folios,
                struct migrate_pages_stats *stats, int nr_pass)
{
        int retry = 1;
        int thp_retry = 1;
        int nr_failed = 0;
        int nr_retry_pages = 0;
        int pass = 0;
        bool is_thp = false;
        struct folio *folio, *folio2, *dst = NULL, *dst2;
        int rc, rc_saved = 0, nr_pages;
        LIST_HEAD(unmap_folios);
        LIST_HEAD(dst_folios);
        bool nosplit = (reason == MR_NUMA_MISPLACED);

        VM_WARN_ON_ONCE(mode != MIGRATE_ASYNC &&
                        !list_empty(from) && !list_is_singular(from));

        for (pass = 0; pass < nr_pass && retry; pass++) {
                retry = 0;
                thp_retry = 0;
                nr_retry_pages = 0;

                list_for_each_entry_safe(folio, folio2, from, lru) {
                        is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
                        nr_pages = folio_nr_pages(folio);

                        cond_resched();

                        /*
                         * Large folio migration might be unsupported or
                         * the allocation might be failed so we should retry
                         * on the same folio with the large folio split
                         * to normal folios.
                         *
                         * Split folios are put in split_folios, and
                         * we will migrate them after the rest of the
                         * list is processed.
                         */
                        if (!thp_migration_supported() && is_thp) {
                                nr_failed++;
                                stats->nr_thp_failed++;
                                if (!try_split_folio(folio, split_folios)) {
                                        stats->nr_thp_split++;
                                        continue;
                                }
                                stats->nr_failed_pages += nr_pages;
                                list_move_tail(&folio->lru, ret_folios);
                                continue;
                        }

                        rc = migrate_folio_unmap(get_new_folio, put_new_folio,
                                        private, folio, &dst, mode, reason,
                                        ret_folios);
                        /*
                         * The rules are:
                         *      Success: folio will be freed
                         *      Unmap: folio will be put on unmap_folios list,
                         *             dst folio put on dst_folios list
                         *      -EAGAIN: stay on the from list
                         *      -ENOMEM: stay on the from list
                         *      Other errno: put on ret_folios list
                         */
                        switch(rc) {
                        case -ENOMEM:
                                /*
                                 * When memory is low, don't bother to try to migrate
                                 * other folios, move unmapped folios, then exit.
                                 */
                                nr_failed++;
                                stats->nr_thp_failed += is_thp;
                                /* Large folio NUMA faulting doesn't split to retry. */
                                if (folio_test_large(folio) && !nosplit) {
                                        int ret = try_split_folio(folio, split_folios);

                                        if (!ret) {
                                                stats->nr_thp_split += is_thp;
                                                break;
                                        } else if (reason == MR_LONGTERM_PIN &&
                                                   ret == -EAGAIN) {
                                                /*
                                                 * Try again to split large folio to
                                                 * mitigate the failure of longterm pinning.
                                                 */
                                                retry++;
                                                thp_retry += is_thp;
                                                nr_retry_pages += nr_pages;
                                                /* Undo duplicated failure counting. */
                                                nr_failed--;
                                                stats->nr_thp_failed -= is_thp;
                                                break;
                                        }
                                }

                                stats->nr_failed_pages += nr_pages + nr_retry_pages;
                                /* nr_failed isn't updated for not used */
                                stats->nr_thp_failed += thp_retry;
                                rc_saved = rc;
                                if (list_empty(&unmap_folios))
                                        goto out;
                                else
                                        goto move;
                        case -EAGAIN:
                                retry++;
                                thp_retry += is_thp;
                                nr_retry_pages += nr_pages;
                                break;
                        case MIGRATEPAGE_SUCCESS:
                                stats->nr_succeeded += nr_pages;
                                stats->nr_thp_succeeded += is_thp;
                                break;
                        case MIGRATEPAGE_UNMAP:
                                list_move_tail(&folio->lru, &unmap_folios);
                                list_add_tail(&dst->lru, &dst_folios);
                                break;
                        default:
                                /*
                                 * Permanent failure (-EBUSY, etc.):
                                 * unlike -EAGAIN case, the failed folio is
                                 * removed from migration folio list and not
                                 * retried in the next outer loop.
                                 */
                                nr_failed++;
                                stats->nr_thp_failed += is_thp;
                                stats->nr_failed_pages += nr_pages;
                                break;
                        }
                }
        }
        nr_failed += retry;
        stats->nr_thp_failed += thp_retry;
        stats->nr_failed_pages += nr_retry_pages;
move:
        /* Flush TLBs for all unmapped folios */
        try_to_unmap_flush();

        retry = 1;
        for (pass = 0; pass < nr_pass && retry; pass++) {
                retry = 0;
                thp_retry = 0;
                nr_retry_pages = 0;

                dst = list_first_entry(&dst_folios, struct folio, lru);
                dst2 = list_next_entry(dst, lru);
                list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) {
                        is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
                        nr_pages = folio_nr_pages(folio);

                        cond_resched();

                        rc = migrate_folio_move(put_new_folio, private,
                                                folio, dst, mode,
                                                reason, ret_folios);
                        /*
                         * The rules are:
                         *      Success: folio will be freed
                         *      -EAGAIN: stay on the unmap_folios list
                         *      Other errno: put on ret_folios list
                         */
                        switch(rc) {
                        case -EAGAIN:
                                retry++;
                                thp_retry += is_thp;
                                nr_retry_pages += nr_pages;
                                break;
                        case MIGRATEPAGE_SUCCESS:
                                stats->nr_succeeded += nr_pages;
                                stats->nr_thp_succeeded += is_thp;
                                break;
                        default:
                                nr_failed++;
                                stats->nr_thp_failed += is_thp;
                                stats->nr_failed_pages += nr_pages;
                                break;
                        }
                        dst = dst2;
                        dst2 = list_next_entry(dst, lru);
                }
        }
        nr_failed += retry;
        stats->nr_thp_failed += thp_retry;
        stats->nr_failed_pages += nr_retry_pages;

        rc = rc_saved ? : nr_failed;
out:
        /* Cleanup remaining folios */
        dst = list_first_entry(&dst_folios, struct folio, lru);
        dst2 = list_next_entry(dst, lru);
        list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) {
                int page_was_mapped = 0;
                struct anon_vma *anon_vma = NULL;

                __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
                migrate_folio_undo_src(folio, page_was_mapped, anon_vma,
                                       true, ret_folios);
                list_del(&dst->lru);
                migrate_folio_undo_dst(dst, true, put_new_folio, private);
                dst = dst2;
                dst2 = list_next_entry(dst, lru);
        }

        return rc;
}

static int migrate_pages_sync(struct list_head *from, new_folio_t get_new_folio,
                free_folio_t put_new_folio, unsigned long private,
                enum migrate_mode mode, int reason,
                struct list_head *ret_folios, struct list_head *split_folios,
                struct migrate_pages_stats *stats)
{
        int rc, nr_failed = 0;
        LIST_HEAD(folios);
        struct migrate_pages_stats astats;

        memset(&astats, 0, sizeof(astats));
        /* Try to migrate in batch with MIGRATE_ASYNC mode firstly */
        rc = migrate_pages_batch(from, get_new_folio, put_new_folio, private, MIGRATE_ASYNC,
                                 reason, &folios, split_folios, &astats,
                                 NR_MAX_MIGRATE_ASYNC_RETRY);
        stats->nr_succeeded += astats.nr_succeeded;
        stats->nr_thp_succeeded += astats.nr_thp_succeeded;
        stats->nr_thp_split += astats.nr_thp_split;
        if (rc < 0) {
                stats->nr_failed_pages += astats.nr_failed_pages;
                stats->nr_thp_failed += astats.nr_thp_failed;
                list_splice_tail(&folios, ret_folios);
                return rc;
        }
        stats->nr_thp_failed += astats.nr_thp_split;
        nr_failed += astats.nr_thp_split;
        /*
         * Fall back to migrate all failed folios one by one synchronously. All
         * failed folios except split THPs will be retried, so their failure
         * isn't counted
         */
        list_splice_tail_init(&folios, from);
        while (!list_empty(from)) {
                list_move(from->next, &folios);
                rc = migrate_pages_batch(&folios, get_new_folio, put_new_folio,
                                         private, mode, reason, ret_folios,
                                         split_folios, stats, NR_MAX_MIGRATE_SYNC_RETRY);
                list_splice_tail_init(&folios, ret_folios);
                if (rc < 0)
                        return rc;
                nr_failed += rc;
        }

        return nr_failed;
}

/*
 * migrate_pages - migrate the folios specified in a list, to the free folios
 *                 supplied as the target for the page migration
 *
 * @from:               The list of folios to be migrated.
 * @get_new_folio:      The function used to allocate free folios to be used
 *                      as the target of the folio migration.
 * @put_new_folio:      The function used to free target folios if migration
 *                      fails, or NULL if no special handling is necessary.
 * @private:            Private data to be passed on to get_new_folio()
 * @mode:               The migration mode that specifies the constraints for
 *                      folio migration, if any.
 * @reason:             The reason for folio migration.
 * @ret_succeeded:      Set to the number of folios migrated successfully if
 *                      the caller passes a non-NULL pointer.
 *
 * The function returns after NR_MAX_MIGRATE_PAGES_RETRY attempts or if no folios
 * are movable any more because the list has become empty or no retryable folios
 * exist any more. It is caller's responsibility to call putback_movable_pages()
 * only if ret != 0.
 *
 * Returns the number of {normal folio, large folio, hugetlb} that were not
 * migrated, or an error code. The number of large folio splits will be
 * considered as the number of non-migrated large folio, no matter how many
 * split folios of the large folio are migrated successfully.
 */
int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
                free_folio_t put_new_folio, unsigned long private,
                enum migrate_mode mode, int reason, unsigned int *ret_succeeded)
{
        int rc, rc_gather;
        int nr_pages;
        struct folio *folio, *folio2;
        LIST_HEAD(folios);
        LIST_HEAD(ret_folios);
        LIST_HEAD(split_folios);
        struct migrate_pages_stats stats;

        trace_mm_migrate_pages_start(mode, reason);

        memset(&stats, 0, sizeof(stats));

        rc_gather = migrate_hugetlbs(from, get_new_folio, put_new_folio, private,
                                     mode, reason, &stats, &ret_folios);
        if (rc_gather < 0)
                goto out;

again:
        nr_pages = 0;
        list_for_each_entry_safe(folio, folio2, from, lru) {
                /* Retried hugetlb folios will be kept in list  */
                if (folio_test_hugetlb(folio)) {
                        list_move_tail(&folio->lru, &ret_folios);
                        continue;
                }

                nr_pages += folio_nr_pages(folio);
                if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
                        break;
        }
        if (nr_pages >= NR_MAX_BATCHED_MIGRATION)
                list_cut_before(&folios, from, &folio2->lru);
        else
                list_splice_init(from, &folios);
        if (mode == MIGRATE_ASYNC)
                rc = migrate_pages_batch(&folios, get_new_folio, put_new_folio,
                                private, mode, reason, &ret_folios,
                                &split_folios, &stats,
                                NR_MAX_MIGRATE_PAGES_RETRY);
        else
                rc = migrate_pages_sync(&folios, get_new_folio, put_new_folio,
                                private, mode, reason, &ret_folios,
                                &split_folios, &stats);
        list_splice_tail_init(&folios, &ret_folios);
        if (rc < 0) {
                rc_gather = rc;
                list_splice_tail(&split_folios, &ret_folios);
                goto out;
        }
        if (!list_empty(&split_folios)) {
                /*
                 * Failure isn't counted since all split folios of a large folio
                 * is counted as 1 failure already.  And, we only try to migrate
                 * with minimal effort, force MIGRATE_ASYNC mode and retry once.
                 */
                migrate_pages_batch(&split_folios, get_new_folio,
                                put_new_folio, private, MIGRATE_ASYNC, reason,
                                &ret_folios, NULL, &stats, 1);
                list_splice_tail_init(&split_folios, &ret_folios);
        }
        rc_gather += rc;
        if (!list_empty(from))
                goto again;
out:
        /*
         * Put the permanent failure folio back to migration list, they
         * will be put back to the right list by the caller.
         */
        list_splice(&ret_folios, from);

        /*
         * Return 0 in case all split folios of fail-to-migrate large folios
         * are migrated successfully.
         */
        if (list_empty(from))
                rc_gather = 0;

        count_vm_events(PGMIGRATE_SUCCESS, stats.nr_succeeded);
        count_vm_events(PGMIGRATE_FAIL, stats.nr_failed_pages);
        count_vm_events(THP_MIGRATION_SUCCESS, stats.nr_thp_succeeded);
        count_vm_events(THP_MIGRATION_FAIL, stats.nr_thp_failed);
        count_vm_events(THP_MIGRATION_SPLIT, stats.nr_thp_split);
        trace_mm_migrate_pages(stats.nr_succeeded, stats.nr_failed_pages,
                               stats.nr_thp_succeeded, stats.nr_thp_failed,
                               stats.nr_thp_split, mode, reason);

        if (ret_succeeded)
                *ret_succeeded = stats.nr_succeeded;

        return rc_gather;
}

struct folio *alloc_migration_target(struct folio *src, unsigned long private)
{
        struct migration_target_control *mtc;
        gfp_t gfp_mask;
        unsigned int order = 0;
        int nid;
        int zidx;

        mtc = (struct migration_target_control *)private;
        gfp_mask = mtc->gfp_mask;
        nid = mtc->nid;
        if (nid == NUMA_NO_NODE)
                nid = folio_nid(src);

        if (folio_test_hugetlb(src)) {
                struct hstate *h = folio_hstate(src);

                gfp_mask = htlb_modify_alloc_mask(h, gfp_mask);
                return alloc_hugetlb_folio_nodemask(h, nid,
                                                mtc->nmask, gfp_mask);
        }

        if (folio_test_large(src)) {
                /*
                 * clear __GFP_RECLAIM to make the migration callback
                 * consistent with regular THP allocations.
                 */
                gfp_mask &= ~__GFP_RECLAIM;
                gfp_mask |= GFP_TRANSHUGE;
                order = folio_order(src);
        }
        zidx = zone_idx(folio_zone(src));
        if (is_highmem_idx(zidx) || zidx == ZONE_MOVABLE)
                gfp_mask |= __GFP_HIGHMEM;

        return __folio_alloc(gfp_mask, order, nid, mtc->nmask);
}

#ifdef CONFIG_NUMA

static int store_status(int __user *status, int start, int value, int nr)
{
        while (nr-- > 0) {
                if (put_user(value, status + start))
                        return -EFAULT;
                start++;
        }

        return 0;
}

static int do_move_pages_to_node(struct mm_struct *mm,
                struct list_head *pagelist, int node)
{
        int err;
        struct migration_target_control mtc = {
                .nid = node,
                .gfp_mask = GFP_HIGHUSER_MOVABLE | __GFP_THISNODE,
        };

        err = migrate_pages(pagelist, alloc_migration_target, NULL,
                (unsigned long)&mtc, MIGRATE_SYNC, MR_SYSCALL, NULL);
        if (err)
                putback_movable_pages(pagelist);
        return err;
}

/*
 * Resolves the given address to a struct page, isolates it from the LRU and
 * puts it to the given pagelist.
 * Returns:
 *     errno - if the page cannot be found/isolated
 *     0 - when it doesn't have to be migrated because it is already on the
 *         target node
 *     1 - when it has been queued
 */
static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
                int node, struct list_head *pagelist, bool migrate_all)
{
        struct vm_area_struct *vma;
        unsigned long addr;
        struct page *page;
        int err;
        bool isolated;

        mmap_read_lock(mm);
        addr = (unsigned long)untagged_addr_remote(mm, p);

        err = -EFAULT;
        vma = vma_lookup(mm, addr);
        if (!vma || !vma_migratable(vma))
                goto out;

        /* FOLL_DUMP to ignore special (like zero) pages */
        page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);

        err = PTR_ERR(page);
        if (IS_ERR(page))
                goto out;

        err = -ENOENT;
        if (!page)
                goto out;

        if (is_zone_device_page(page))
                goto out_putpage;

        err = 0;
        if (page_to_nid(page) == node)
                goto out_putpage;

        err = -EACCES;
        if (page_mapcount(page) > 1 && !migrate_all)
                goto out_putpage;

        if (PageHuge(page)) {
                if (PageHead(page)) {
                        isolated = isolate_hugetlb(page_folio(page), pagelist);
                        err = isolated ? 1 : -EBUSY;
                }
        } else {
                struct page *head;

                head = compound_head(page);
                isolated = isolate_lru_page(head);
                if (!isolated) {
                        err = -EBUSY;
                        goto out_putpage;
                }

                err = 1;
                list_add_tail(&head->lru, pagelist);
                mod_node_page_state(page_pgdat(head),
                        NR_ISOLATED_ANON + page_is_file_lru(head),
                        thp_nr_pages(head));
        }
out_putpage:
        /*
         * Either remove the duplicate refcount from
         * isolate_lru_page() or drop the page ref if it was
         * not isolated.
         */
        put_page(page);
out:
        mmap_read_unlock(mm);
        return err;
}

static int move_pages_and_store_status(struct mm_struct *mm, int node,
                struct list_head *pagelist, int __user *status,
                int start, int i, unsigned long nr_pages)
{
        int err;

        if (list_empty(pagelist))
                return 0;

        err = do_move_pages_to_node(mm, pagelist, node);
        if (err) {
                /*
                 * Positive err means the number of failed
                 * pages to migrate.  Since we are going to
                 * abort and return the number of non-migrated
                 * pages, so need to include the rest of the
                 * nr_pages that have not been attempted as
                 * well.
                 */
                if (err > 0)
                        err += nr_pages - i;
                return err;
        }
        return store_status(status, start, node, i - start);
}

/*
 * Migrate an array of page address onto an array of nodes and fill
 * the corresponding array of status.
 */
static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
                         unsigned long nr_pages,
                         const void __user * __user *pages,
                         const int __user *nodes,
                         int __user *status, int flags)
{
        int current_node = NUMA_NO_NODE;
        LIST_HEAD(pagelist);
        int start, i;
        int err = 0, err1;

        lru_cache_disable();

        for (i = start = 0; i < nr_pages; i++) {
                const void __user *p;
                int node;

                err = -EFAULT;
                if (get_user(p, pages + i))
                        goto out_flush;
                if (get_user(node, nodes + i))
                        goto out_flush;

                err = -ENODEV;
                if (node < 0 || node >= MAX_NUMNODES)
                        goto out_flush;
                if (!node_state(node, N_MEMORY))
                        goto out_flush;

                err = -EACCES;
                if (!node_isset(node, task_nodes))
                        goto out_flush;

                if (current_node == NUMA_NO_NODE) {
                        current_node = node;
                        start = i;
                } else if (node != current_node) {
                        err = move_pages_and_store_status(mm, current_node,
                                        &pagelist, status, start, i, nr_pages);
                        if (err)
                                goto out;
                        start = i;
                        current_node = node;
                }

                /*
                 * Errors in the page lookup or isolation are not fatal and we simply
                 * report them via status
                 */
                err = add_page_for_migration(mm, p, current_node, &pagelist,
                                             flags & MPOL_MF_MOVE_ALL);

                if (err > 0) {
                        /* The page is successfully queued for migration */
                        continue;
                }

                /*
                 * The move_pages() man page does not have an -EEXIST choice, so
                 * use -EFAULT instead.
                 */
                if (err == -EEXIST)
                        err = -EFAULT;

                /*
                 * If the page is already on the target node (!err), store the
                 * node, otherwise, store the err.
                 */
                err = store_status(status, i, err ? : current_node, 1);
                if (err)
                        goto out_flush;

                err = move_pages_and_store_status(mm, current_node, &pagelist,
                                status, start, i, nr_pages);
                if (err) {
                        /* We have accounted for page i */
                        if (err > 0)
                                err--;
                        goto out;
                }
                current_node = NUMA_NO_NODE;
        }
out_flush:
        /* Make sure we do not overwrite the existing error */
        err1 = move_pages_and_store_status(mm, current_node, &pagelist,
                                status, start, i, nr_pages);
        if (err >= 0)
                err = err1;
out:
        lru_cache_enable();
        return err;
}

/*
 * Determine the nodes of an array of pages and store it in an array of status.
 */
static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
                                const void __user **pages, int *status)
{
        unsigned long i;

        mmap_read_lock(mm);

        for (i = 0; i < nr_pages; i++) {
                unsigned long addr = (unsigned long)(*pages);
                struct vm_area_struct *vma;
                struct page *page;
                int err = -EFAULT;

                vma = vma_lookup(mm, addr);
                if (!vma)
                        goto set_status;

                /* FOLL_DUMP to ignore special (like zero) pages */
                page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);

                err = PTR_ERR(page);
                if (IS_ERR(page))
                        goto set_status;

                err = -ENOENT;
                if (!page)
                        goto set_status;

                if (!is_zone_device_page(page))
                        err = page_to_nid(page);

                put_page(page);
set_status:
                *status = err;

                pages++;
                status++;
        }

        mmap_read_unlock(mm);
}

static int get_compat_pages_array(const void __user *chunk_pages[],
                                  const void __user * __user *pages,
                                  unsigned long chunk_nr)
{
        compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
        compat_uptr_t p;
        int i;

        for (i = 0; i < chunk_nr; i++) {
                if (get_user(p, pages32 + i))
                        return -EFAULT;
                chunk_pages[i] = compat_ptr(p);
        }

        return 0;
}

/*
 * Determine the nodes of a user array of pages and store it in
 * a user array of status.
 */
static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
                         const void __user * __user *pages,
                         int __user *status)
{
#define DO_PAGES_STAT_CHUNK_NR 16UL
        const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
        int chunk_status[DO_PAGES_STAT_CHUNK_NR];

        while (nr_pages) {
                unsigned long chunk_nr = min(nr_pages, DO_PAGES_STAT_CHUNK_NR);

                if (in_compat_syscall()) {
                        if (get_compat_pages_array(chunk_pages, pages,
                                                   chunk_nr))
                                break;
                } else {
                        if (copy_from_user(chunk_pages, pages,
                                      chunk_nr * sizeof(*chunk_pages)))
                                break;
                }

                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);

                if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
                        break;

                pages += chunk_nr;
                status += chunk_nr;
                nr_pages -= chunk_nr;
        }
        return nr_pages ? -EFAULT : 0;
}

static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes)
{
        struct task_struct *task;
        struct mm_struct *mm;

        /*
         * There is no need to check if current process has the right to modify
         * the specified process when they are same.
         */
        if (!pid) {
                mmget(current->mm);
                *mem_nodes = cpuset_mems_allowed(current);
                return current->mm;
        }

        /* Find the mm_struct */
        rcu_read_lock();
        task = find_task_by_vpid(pid);
        if (!task) {
                rcu_read_unlock();
                return ERR_PTR(-ESRCH);
        }
        get_task_struct(task);

        /*
         * Check if this process has the right to modify the specified
         * process. Use the regular "ptrace_may_access()" checks.
         */
        if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
                rcu_read_unlock();
                mm = ERR_PTR(-EPERM);
                goto out;
        }
        rcu_read_unlock();

        mm = ERR_PTR(security_task_movememory(task));
        if (IS_ERR(mm))
                goto out;
        *mem_nodes = cpuset_mems_allowed(task);
        mm = get_task_mm(task);
out:
        put_task_struct(task);
        if (!mm)
                mm = ERR_PTR(-EINVAL);
        return mm;
}

/*
 * Move a list of pages in the address space of the currently executing
 * process.
 */
static int kernel_move_pages(pid_t pid, unsigned long nr_pages,
                             const void __user * __user *pages,
                             const int __user *nodes,
                             int __user *status, int flags)
{
        struct mm_struct *mm;
        int err;
        nodemask_t task_nodes;

        /* Check flags */
        if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
                return -EINVAL;

        if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
                return -EPERM;

        mm = find_mm_struct(pid, &task_nodes);
        if (IS_ERR(mm))
                return PTR_ERR(mm);

        if (nodes)
                err = do_pages_move(mm, task_nodes, nr_pages, pages,
                                    nodes, status, flags);
        else
                err = do_pages_stat(mm, nr_pages, pages, status);

        mmput(mm);
        return err;
}

SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
                const void __user * __user *, pages,
                const int __user *, nodes,
                int __user *, status, int, flags)
{
        return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
}

#ifdef CONFIG_NUMA_BALANCING
/*
 * Returns true if this is a safe migration target node for misplaced NUMA
 * pages. Currently it only checks the watermarks which is crude.
 */
static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
                                   unsigned long nr_migrate_pages)
{
        int z;

        for (z = pgdat->nr_zones - 1; z >= 0; z--) {
                struct zone *zone = pgdat->node_zones + z;

                if (!managed_zone(zone))
                        continue;

                /* Avoid waking kswapd by allocating pages_to_migrate pages. */
                if (!zone_watermark_ok(zone, 0,
                                       high_wmark_pages(zone) +
                                       nr_migrate_pages,
                                       ZONE_MOVABLE, 0))
                        continue;
                return true;
        }
        return false;
}

static struct folio *alloc_misplaced_dst_folio(struct folio *src,
                                           unsigned long data)
{
        int nid = (int) data;
        int order = folio_order(src);
        gfp_t gfp = __GFP_THISNODE;

        if (order > 0)
                gfp |= GFP_TRANSHUGE_LIGHT;
        else {
                gfp |= GFP_HIGHUSER_MOVABLE | __GFP_NOMEMALLOC | __GFP_NORETRY |
                        __GFP_NOWARN;
                gfp &= ~__GFP_RECLAIM;
        }
        return __folio_alloc_node(gfp, order, nid);
}

static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
{
        int nr_pages = thp_nr_pages(page);
        int order = compound_order(page);

        VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);

        /* Do not migrate THP mapped by multiple processes */
        if (PageTransHuge(page) && total_mapcount(page) > 1)
                return 0;

        /* Avoid migrating to a node that is nearly full */
        if (!migrate_balanced_pgdat(pgdat, nr_pages)) {
                int z;

                if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING))
                        return 0;
                for (z = pgdat->nr_zones - 1; z >= 0; z--) {
                        if (managed_zone(pgdat->node_zones + z))
                                break;
                }
                wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE);
                return 0;
        }

        if (!isolate_lru_page(page))
                return 0;

        mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_is_file_lru(page),
                            nr_pages);

        /*
         * Isolating the page has taken another reference, so the
         * caller's reference can be safely dropped without the page
         * disappearing underneath us during migration.
         */
        put_page(page);
        return 1;
}

/*
 * Attempt to migrate a misplaced page to the specified destination
 * node. Caller is expected to have an elevated reference count on
 * the page that will be dropped by this function before returning.
 */
int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
                           int node)
{
        pg_data_t *pgdat = NODE_DATA(node);
        int isolated;
        int nr_remaining;
        unsigned int nr_succeeded;
        LIST_HEAD(migratepages);
        int nr_pages = thp_nr_pages(page);

        /*
         * Don't migrate file pages that are mapped in multiple processes
         * with execute permissions as they are probably shared libraries.
         */
        if (page_mapcount(page) != 1 && page_is_file_lru(page) &&
            (vma->vm_flags & VM_EXEC))
                goto out;

        /*
         * Also do not migrate dirty pages as not all filesystems can move
         * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
         */
        if (page_is_file_lru(page) && PageDirty(page))
                goto out;

        isolated = numamigrate_isolate_page(pgdat, page);
        if (!isolated)
                goto out;

        list_add(&page->lru, &migratepages);
        nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_folio,
                                     NULL, node, MIGRATE_ASYNC,
                                     MR_NUMA_MISPLACED, &nr_succeeded);
        if (nr_remaining) {
                if (!list_empty(&migratepages)) {
                        list_del(&page->lru);
                        mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
                                        page_is_file_lru(page), -nr_pages);
                        putback_lru_page(page);
                }
                isolated = 0;
        }
        if (nr_succeeded) {
                count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
                if (!node_is_toptier(page_to_nid(page)) && node_is_toptier(node))
                        mod_node_page_state(pgdat, PGPROMOTE_SUCCESS,
                                            nr_succeeded);
        }
        BUG_ON(!list_empty(&migratepages));
        return isolated;

out:
        put_page(page);
        return 0;
}
#endif /* CONFIG_NUMA_BALANCING */
#endif /* CONFIG_NUMA */