migrate_pages: split unmap_and_move() to _unmap() and _move()

This is a preparation patch to batch the folio unmapping and moving.

In this patch, unmap_and_move() is split to migrate_folio_unmap() and
migrate_folio_move().  So, we can batch _unmap() and _move() in different
loops later.  To pass some information between unmap and move, the
original unused dst->mapping and dst->private are used.

Link: https://lkml.kernel.org/r/20230213123444.155149-5-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index bdff950a8bb45955ab2b7cc88cad481f85bbfb80..c88b96b48be706b0980e3f99433996e62a31fde8 100644 (file)
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -18,6 +18,7 @@ struct migration_target_control;
  * - zero on page migration success;
  */
 #define MIGRATEPAGE_SUCCESS            0
+#define MIGRATEPAGE_UNMAP              1
 
 /**
  * struct movable_operations - Driver page migration

diff --git a/mm/migrate.c b/mm/migrate.c
index d436f35fa145a4636f47d414ee9ab07ff7e42cee..5fd18a7cce62b84e6977b7a4de2535301113f547 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1027,11 +1027,53 @@ out:
        return rc;
 }
 
-static int __unmap_and_move(struct folio *src, struct folio *dst,
+/*
+ * 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.
+ */
+static void __migrate_folio_record(struct folio *dst,
+                                  unsigned long page_was_mapped,
+                                  struct anon_vma *anon_vma)
+{
+       dst->mapping = (void *)anon_vma;
+       dst->private = (void *)page_was_mapped;
+}
+
+static void __migrate_folio_extract(struct folio *dst,
+                                  int *page_was_mappedp,
+                                  struct anon_vma **anon_vmap)
+{
+       *anon_vmap = (void *)dst->mapping;
+       *page_was_mappedp = (unsigned long)dst->private;
+       dst->mapping = NULL;
+       dst->private = NULL;
+}
+
+/* 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);
+}
+
+static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
                                int force, enum migrate_mode mode)
 {
        int rc = -EAGAIN;
-       bool page_was_mapped = false;
+       int page_was_mapped = 0;
        struct anon_vma *anon_vma = NULL;
        bool is_lru = !__PageMovable(&src->page);
 
@@ -1107,8 +1149,8 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
                goto out_unlock;
 
        if (unlikely(!is_lru)) {
-               rc = move_to_new_folio(dst, src, mode);
-               goto out_unlock_both;
+               __migrate_folio_record(dst, page_was_mapped, anon_vma);
+               return MIGRATEPAGE_UNMAP;
        }
 
        /*
@@ -1133,11 +1175,42 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
                VM_BUG_ON_FOLIO(folio_test_anon(src) &&
                               !folio_test_ksm(src) && !anon_vma, src);
                try_to_migrate(src, 0);
-               page_was_mapped = true;
+               page_was_mapped = 1;
        }
 
-       if (!folio_mapped(src))
-               rc = move_to_new_folio(dst, src, mode);
+       if (!folio_mapped(src)) {
+               __migrate_folio_record(dst, page_was_mapped, anon_vma);
+               return MIGRATEPAGE_UNMAP;
+       }
+
+       if (page_was_mapped)
+               remove_migration_ptes(src, src, false);
+
+out_unlock_both:
+       folio_unlock(dst);
+out_unlock:
+       /* Drop an anon_vma reference if we took one */
+       if (anon_vma)
+               put_anon_vma(anon_vma);
+       folio_unlock(src);
+out:
+
+       return rc;
+}
+
+static int __migrate_folio_move(struct folio *src, struct folio *dst,
+                               enum migrate_mode mode)
+{
+       int rc;
+       int page_was_mapped = 0;
+       struct anon_vma *anon_vma = NULL;
+       bool is_lru = !__PageMovable(&src->page);
+
+       __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
+
+       rc = move_to_new_folio(dst, src, mode);
+       if (unlikely(!is_lru))
+               goto out_unlock_both;
 
        /*
         * When successful, push dst to LRU immediately: so that if it
@@ -1160,12 +1233,10 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
 
 out_unlock_both:
        folio_unlock(dst);
-out_unlock:
        /* Drop an anon_vma reference if we took one */
        if (anon_vma)
                put_anon_vma(anon_vma);
        folio_unlock(src);
-out:
        /*
         * If migration is successful, decrease refcount of dst,
         * which will not free the page because new page owner increased
@@ -1177,19 +1248,15 @@ out:
        return rc;
 }
 
-/*
- * Obtain the lock on folio, remove all ptes and migrate the folio
- * to the newly allocated folio in dst.
- */
-static int unmap_and_move(new_page_t get_new_page,
-                                  free_page_t put_new_page,
-                                  unsigned long private, struct folio *src,
-                                  int force, enum migrate_mode mode,
-                                  enum migrate_reason reason,
-                                  struct list_head *ret)
+/* Obtain the lock on page, remove all ptes. */
+static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page,
+                              unsigned long private, struct folio *src,
+                              struct folio **dstp, int force,
+                              enum migrate_mode mode, enum migrate_reason reason,
+                              struct list_head *ret)
 {
        struct folio *dst;
-       int rc = MIGRATEPAGE_SUCCESS;
+       int rc = MIGRATEPAGE_UNMAP;
        struct page *newpage = NULL;
 
        if (!thp_migration_supported() && folio_test_transhuge(src))
@@ -1200,20 +1267,49 @@ static int unmap_and_move(new_page_t get_new_page,
                folio_clear_active(src);
                folio_clear_unevictable(src);
                /* free_pages_prepare() will clear PG_isolated. */
-               goto out;
+               list_del(&src->lru);
+               migrate_folio_done(src, reason);
+               return MIGRATEPAGE_SUCCESS;
        }
 
        newpage = get_new_page(&src->page, private);
        if (!newpage)
                return -ENOMEM;
        dst = page_folio(newpage);
+       *dstp = dst;
 
        dst->private = NULL;
-       rc = __unmap_and_move(src, dst, force, mode);
+       rc = __migrate_folio_unmap(src, dst, force, mode);
+       if (rc == MIGRATEPAGE_UNMAP)
+               return rc;
+
+       /*
+        * A folio that has not been unmapped will be restored to
+        * right list unless we want to retry.
+        */
+       if (rc != -EAGAIN)
+               list_move_tail(&src->lru, ret);
+
+       if (put_new_page)
+               put_new_page(&dst->page, private);
+       else
+               folio_put(dst);
+
+       return rc;
+}
+
+/* Migrate the folio to the newly allocated folio in dst. */
+static int migrate_folio_move(free_page_t put_new_page, unsigned long private,
+                             struct folio *src, struct folio *dst,
+                             enum migrate_mode mode, enum migrate_reason reason,
+                             struct list_head *ret)
+{
+       int rc;
+
+       rc = __migrate_folio_move(src, dst, mode);
        if (rc == MIGRATEPAGE_SUCCESS)
                set_page_owner_migrate_reason(&dst->page, reason);
 
-out:
        if (rc != -EAGAIN) {
                /*
                 * A folio that has been migrated has all references
@@ -1229,20 +1325,7 @@ out:
         * we want to retry.
         */
        if (rc == MIGRATEPAGE_SUCCESS) {
-               /*
-                * Compaction can migrate also non-LRU folios which are
-                * not accounted to NR_ISOLATED_*. They can be recognized
-                * as __folio_test_movable
-                */
-               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 folio in page_handle_poison.
-                        */
-                       folio_put(src);
+               migrate_folio_done(src, reason);
        } else {
                if (rc != -EAGAIN)
                        list_add_tail(&src->lru, ret);
@@ -1534,7 +1617,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
        int pass = 0;
        bool is_large = false;
        bool is_thp = false;
-       struct folio *folio, *folio2;
+       struct folio *folio, *folio2, *dst = NULL;
        int rc, nr_pages;
        LIST_HEAD(split_folios);
        bool nosplit = (reason == MR_NUMA_MISPLACED);
@@ -1561,9 +1644,13 @@ split_folio_migration:
 
                        cond_resched();
 
-                       rc = unmap_and_move(get_new_page, put_new_page,
-                                           private, folio, pass > 2, mode,
-                                           reason, ret_folios);
+                       rc = migrate_folio_unmap(get_new_page, put_new_page, private,
+                                                folio, &dst, pass > 2, mode,
+                                                reason, ret_folios);
+                       if (rc == MIGRATEPAGE_UNMAP)
+                               rc = migrate_folio_move(put_new_page, private,
+                                                       folio, dst, mode,
+                                                       reason, ret_folios);
                        /*
                         * The rules are:
                         *      Success: folio will be freed