[PATCH 4/8] migrate_pages: split unmap_and_move() to _unmap() and _move()

Huang Ying
2022-12-27T00:30:39Z

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.

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.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: haoxin <xhao@linux.alibaba.com>
---
include/linux/migrate.h | 1 +
mm/migrate.c | 162 +++++++++++++++++++++++++++++-----------
2 files changed, 121 insertions(+), 42 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 3ef77f52a4f0..7376074f2e1e 100644
--- 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 97ea0737ab2b..e2383b430932 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1009,11 +1009,29 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
return rc;
}

-static int __unmap_and_move(struct folio *src, struct folio *dst,
+static void __migrate_folio_record(struct folio *dst,
+ unsigned long page_was_mapped,
+ struct anon_vma *anon_vma)
+{
+ dst->mapping = (struct address_space *)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 = (struct anon_vma *)dst->mapping;
+ *page_was_mappedp = (unsigned long)dst->private;
+ dst->mapping = NULL;
+ dst->private = NULL;
+}
+
+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);

@@ -1089,8 +1107,8 @@ 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;
}

/*
@@ -1115,11 +1133,40 @@ 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;
+
+ __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
+
+ rc = move_to_new_folio(dst, src, mode);

/*
* When successful, push dst to LRU immediately: so that if it
@@ -1140,14 +1187,11 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
remove_migration_ptes(src,
rc == MIGRATEPAGE_SUCCESS ? dst : 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:
/*
* If migration is successful, decrease refcount of dst,
* which will not free the page because new page owner increased
@@ -1159,19 +1203,32 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
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)
+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_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))
@@ -1182,20 +1239,50 @@ 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 page that has not been migrated will have kept its
+ * references and be restored.
+ */
+ /* restore the folio to right list. */
+ 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
@@ -1211,20 +1298,7 @@ static int unmap_and_move(new_page_t get_new_page,
* 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);
@@ -1499,7 +1573,7 @@ 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);
@@ -1524,9 +1598,13 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,

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
--
2.35.1