From d50791c2bee9ed97b1dd81db9bbb11caddcdfb0d Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 11 Jul 2023 21:43:36 -0700 Subject: [PATCH] mm/khugepaged: delete khugepaged_collapse_pte_mapped_thps() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Now that retract_page_tables() can retract page tables reliably, without depending on trylocks, delete all the apparatus for khugepaged to try again later: khugepaged_collapse_pte_mapped_thps() etc; and free up the per-mm memory which was set aside for that in the khugepaged_mm_slot. But one part of that is worth keeping: when hpage_collapse_scan_file() found SCAN_PTE_MAPPED_HUGEPAGE, that address was noted in the mm_slot to be tried for retraction later - catching, for example, page tables where a reversible mprotect() of a portion had required splitting the pmd, but now it can be recollapsed. Call collapse_pte_mapped_thp() directly in this case (why was it deferred before? I assume an issue with needing mmap_lock for write, but now it's only needed for read). [hughd@google.com: fix mmap_locked handlng] Link: https://lkml.kernel.org/r/bfc6cab2-497f-32bf-dd5-98dc1987e4a9@google.com Link: https://lkml.kernel.org/r/a5dce57-6dfa-5559-4698-e817eb2f993@google.com Signed-off-by: Hugh Dickins Cc: Alexander Gordeev Cc: Alistair Popple Cc: Aneesh Kumar K.V Cc: Anshuman Khandual Cc: Axel Rasmussen Cc: Christian Borntraeger Cc: Christophe Leroy Cc: Christoph Hellwig Cc: Claudio Imbrenda Cc: David Hildenbrand Cc: "David S. Miller" Cc: Gerald Schaefer Cc: Heiko Carstens Cc: Huang, Ying Cc: Ira Weiny Cc: Jann Horn Cc: Jason Gunthorpe Cc: Kirill A. Shutemov Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Mel Gorman Cc: Miaohe Lin Cc: Michael Ellerman Cc: Mike Kravetz Cc: Mike Rapoport (IBM) Cc: Minchan Kim Cc: Naoya Horiguchi Cc: Pavel Tatashin Cc: Peter Xu Cc: Peter Zijlstra Cc: Qi Zheng Cc: Ralph Campbell Cc: Russell King Cc: SeongJae Park Cc: Song Liu Cc: Steven Price Cc: Suren Baghdasaryan Cc: Thomas Hellström Cc: Vasily Gorbik Cc: Vishal Moola (Oracle) Cc: Vlastimil Babka Cc: Will Deacon Cc: Yang Shi Cc: Yu Zhao Cc: Zack Rusin Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/khugepaged.c | 125 +++++++------------------------------------------------- 1 file changed, 15 insertions(+), 110 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 53d1788..9a6e0d5 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -93,8 +93,6 @@ static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); static struct kmem_cache *mm_slot_cache __read_mostly; -#define MAX_PTE_MAPPED_THP 8 - struct collapse_control { bool is_khugepaged; @@ -108,15 +106,9 @@ struct collapse_control { /** * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned * @slot: hash lookup from mm to mm_slot - * @nr_pte_mapped_thp: number of pte mapped THP - * @pte_mapped_thp: address array corresponding pte mapped THP */ struct khugepaged_mm_slot { struct mm_slot slot; - - /* pte-mapped THP in this mm */ - int nr_pte_mapped_thp; - unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP]; }; /** @@ -1441,50 +1433,6 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot) } #ifdef CONFIG_SHMEM -/* - * Notify khugepaged that given addr of the mm is pte-mapped THP. Then - * khugepaged should try to collapse the page table. - * - * Note that following race exists: - * (1) khugepaged calls khugepaged_collapse_pte_mapped_thps() for mm_struct A, - * emptying the A's ->pte_mapped_thp[] array. - * (2) MADV_COLLAPSE collapses some file extent with target mm_struct B, and - * retract_page_tables() finds a VMA in mm_struct A mapping the same extent - * (at virtual address X) and adds an entry (for X) into mm_struct A's - * ->pte-mapped_thp[] array. - * (3) khugepaged calls khugepaged_collapse_scan_file() for mm_struct A at X, - * sees a pte-mapped THP (SCAN_PTE_MAPPED_HUGEPAGE) and adds an entry - * (for X) into mm_struct A's ->pte-mapped_thp[] array. - * Thus, it's possible the same address is added multiple times for the same - * mm_struct. Should this happen, we'll simply attempt - * collapse_pte_mapped_thp() multiple times for the same address, under the same - * exclusive mmap_lock, and assuming the first call is successful, subsequent - * attempts will return quickly (without grabbing any additional locks) when - * a huge pmd is found in find_pmd_or_thp_or_none(). Since this is a cheap - * check, and since this is a rare occurrence, the cost of preventing this - * "multiple-add" is thought to be more expensive than just handling it, should - * it occur. - */ -static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm, - unsigned long addr) -{ - struct khugepaged_mm_slot *mm_slot; - struct mm_slot *slot; - bool ret = false; - - VM_BUG_ON(addr & ~HPAGE_PMD_MASK); - - spin_lock(&khugepaged_mm_lock); - slot = mm_slot_lookup(mm_slots_hash, mm); - mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot); - if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) { - mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr; - ret = true; - } - spin_unlock(&khugepaged_mm_lock); - return ret; -} - /* hpage must be locked, and mmap_lock must be held */ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp, struct page *hpage) @@ -1708,29 +1656,6 @@ drop_hpage: return result; } -static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot) -{ - struct mm_slot *slot = &mm_slot->slot; - struct mm_struct *mm = slot->mm; - int i; - - if (likely(mm_slot->nr_pte_mapped_thp == 0)) - return; - - if (!mmap_write_trylock(mm)) - return; - - if (unlikely(hpage_collapse_test_exit(mm))) - goto out; - - for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++) - collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i], false); - -out: - mm_slot->nr_pte_mapped_thp = 0; - mmap_write_unlock(mm); -} - static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) { struct vm_area_struct *vma; @@ -2371,16 +2296,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, { BUILD_BUG(); } - -static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot) -{ -} - -static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm, - unsigned long addr) -{ - return false; -} #endif static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, @@ -2410,7 +2325,6 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result, khugepaged_scan.mm_slot = mm_slot; } spin_unlock(&khugepaged_mm_lock); - khugepaged_collapse_pte_mapped_thps(mm_slot); mm = slot->mm; /* @@ -2463,36 +2377,27 @@ skip: khugepaged_scan.address); mmap_read_unlock(mm); - *result = hpage_collapse_scan_file(mm, - khugepaged_scan.address, - file, pgoff, cc); mmap_locked = false; + *result = hpage_collapse_scan_file(mm, + khugepaged_scan.address, file, pgoff, cc); fput(file); + if (*result == SCAN_PTE_MAPPED_HUGEPAGE) { + mmap_read_lock(mm); + if (hpage_collapse_test_exit(mm)) + goto breakouterloop; + *result = collapse_pte_mapped_thp(mm, + khugepaged_scan.address, false); + if (*result == SCAN_PMD_MAPPED) + *result = SCAN_SUCCEED; + mmap_read_unlock(mm); + } } else { *result = hpage_collapse_scan_pmd(mm, vma, - khugepaged_scan.address, - &mmap_locked, - cc); + khugepaged_scan.address, &mmap_locked, cc); } - switch (*result) { - case SCAN_PTE_MAPPED_HUGEPAGE: { - pmd_t *pmd; - - *result = find_pmd_or_thp_or_none(mm, - khugepaged_scan.address, - &pmd); - if (*result != SCAN_SUCCEED) - break; - if (!khugepaged_add_pte_mapped_thp(mm, - khugepaged_scan.address)) - break; - } fallthrough; - case SCAN_SUCCEED: + + if (*result == SCAN_SUCCEED) ++khugepaged_pages_collapsed; - break; - default: - break; - } /* move to next address */ khugepaged_scan.address += HPAGE_PMD_SIZE; -- 2.7.4