[PATCH 7/8] migrate_pages: share more code between _unmap and _move

Huang Ying
2022-12-27T00:31:11Z

This is a code cleanup patch to reduce the duplicated code between the
_unmap and _move stages of migrate_pages(). No functionality change
is expected.

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>
---
mm/migrate.c | 208 ++++++++++++++++++++-------------------------------
1 file changed, 82 insertions(+), 126 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 70b987391296..70a40b8fee1f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1030,21 +1030,26 @@ static void __migrate_folio_extract(struct folio *dst,
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);
if (anon_vma)
put_anon_vma(anon_vma);
- folio_unlock(src);
- list_move_tail(&src->lru, ret);
+ if (locked)
+ folio_unlock(src);
+ if (ret)
+ list_move_tail(&src->lru, ret);
}

static void migrate_folio_undo_dst(struct folio *dst,
+ bool locked,
free_page_t put_new_page,
unsigned long private)
{
- folio_unlock(dst);
+ if (locked)
+ folio_unlock(dst);
if (put_new_page)
put_new_page(&dst->page, private);
else
@@ -1068,14 +1073,44 @@ static void migrate_folio_done(struct folio *src,
folio_put(src);
}

-static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
- int force, bool force_lock, enum migrate_mode mode)
+/* 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, bool force_lock,
+ enum migrate_mode mode, enum migrate_reason reason,
+ struct list_head *ret)
{
- int rc = -EAGAIN;
+ struct folio *dst;
+ int rc = MIGRATEPAGE_UNMAP;
+ struct page *newpage = NULL;
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 (!thp_migration_supported() && folio_test_transhuge(src))
+ return -ENOSYS;
+
+ 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;
+ }
+
+ newpage = get_new_page(&src->page, private);
+ if (!newpage)
+ return -ENOMEM;
+ dst = page_folio(newpage);
+ *dstp = dst;
+
+ dst->private = NULL;

+ rc = -EAGAIN;
if (!folio_trylock(src)) {
if (!force || mode == MIGRATE_ASYNC)
goto out;
@@ -1103,6 +1138,7 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,

folio_lock(src);
}
+ locked = true;

if (folio_test_writeback(src)) {
/*
@@ -1117,10 +1153,10 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
break;
default:
rc = -EBUSY;
- goto out_unlock;
+ goto out;
}
if (!force)
- goto out_unlock;
+ goto out;
folio_wait_writeback(src);
}

@@ -1150,7 +1186,8 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
* This is much like races on refcount of oldpage: just don't BUG().
*/
if (unlikely(!folio_trylock(dst)))
- goto out_unlock;
+ goto out;
+ dst_locked = true;

if (unlikely(!is_lru)) {
__migrate_folio_record(dst, page_was_mapped, anon_vma);
@@ -1172,7 +1209,7 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
if (!src->mapping) {
if (folio_test_private(src)) {
try_to_free_buffers(src);
- goto out_unlock_both;
+ goto out;
}
} else if (folio_mapped(src)) {
/* Establish migration ptes */
@@ -1187,75 +1224,27 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
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;
-}
-
-/* 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, bool force_lock,
- enum migrate_mode mode, enum migrate_reason reason,
- struct list_head *ret)
-{
- struct folio *dst;
- int rc = MIGRATEPAGE_UNMAP;
- struct page *newpage = NULL;
-
- if (!thp_migration_supported() && folio_test_transhuge(src))
- return -ENOSYS;
-
- 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;
- }
-
- newpage = get_new_page(&src->page, private);
- if (!newpage)
- return -ENOMEM;
- dst = page_folio(newpage);
- *dstp = dst;
-
- dst->private = NULL;
- rc = __migrate_folio_unmap(src, dst, force, force_lock, 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 && rc != -EDEADLOCK)
- list_move_tail(&src->lru, ret);
+ if (rc == -EAGAIN || rc == -EDEADLOCK)
+ ret = NULL;

- if (put_new_page)
- put_new_page(&dst->page, private);
- else
- folio_put(dst);
+ migrate_folio_undo_src(src, page_was_mapped, anon_vma, locked, ret);
+ if (dst)
+ migrate_folio_undo_dst(dst, dst_locked, put_new_page, private);

return rc;
}

-static int __migrate_folio_move(struct folio *src, struct folio *dst,
- enum migrate_mode mode)
+/* 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;
int page_was_mapped = 0;
@@ -1264,9 +1253,10 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,
__migrate_folio_extract(dst, &page_was_mapped, &anon_vma);

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

- if (rc != -EAGAIN)
- list_del(&dst->lru);
+ list_del(&dst->lru);
/*
* When successful, push dst to LRU immediately: so that if it
* turns out to be an mlocked page, remove_migration_ptes() will
@@ -1276,74 +1266,40 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,
* unsuccessful, and other cases when a page has been temporarily
* isolated from the unevictable LRU: but this case is the easiest.
*/
- if (rc == MIGRATEPAGE_SUCCESS) {
- folio_add_lru(dst);
- if (page_was_mapped)
- lru_add_drain();
- }
-
- if (rc == -EAGAIN) {
- __migrate_folio_record(dst, page_was_mapped, anon_vma);
- return rc;
- }
-
+ folio_add_lru(dst);
if (page_was_mapped)
- remove_migration_ptes(src,
- rc == MIGRATEPAGE_SUCCESS ? dst : src, false);
+ lru_add_drain();

+ if (page_was_mapped)
+ remove_migration_ptes(src, dst, false);
folio_unlock(dst);
- /* Drop an anon_vma reference if we took one */
- if (anon_vma)
- put_anon_vma(anon_vma);
- folio_unlock(src);
+ 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.
*/
- if (rc == MIGRATEPAGE_SUCCESS)
- 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);
-
- if (rc != -EAGAIN) {
- /*
- * A folio that has been migrated has all references
- * removed and will be freed. A folio that has not been
- * migrated will have kept its references and be restored.
- */
- list_del(&src->lru);
- }
+ folio_put(dst);

/*
- * If migration is successful, releases reference grabbed during
- * isolation. Otherwise, restore the folio to right list unless
- * we want to retry.
+ * A page that has been migrated has all references removed
+ * and will be freed.
*/
- if (rc == MIGRATEPAGE_SUCCESS) {
- migrate_folio_done(src, reason);
- } else if (rc != -EAGAIN) {
- list_add_tail(&src->lru, ret);
+ list_del(&src->lru);
+ migrate_folio_undo_src(src, 0, anon_vma, true, NULL);
+ migrate_folio_done(src, reason);

- if (put_new_page)
- put_new_page(&dst->page, private);
- else
- folio_put(dst);
+ return rc;
+out:
+ if (rc == -EAGAIN) {
+ __migrate_folio_record(dst, page_was_mapped, anon_vma);
+ return rc;
}

+ migrate_folio_undo_src(src, page_was_mapped, anon_vma, true, ret);
+ list_del(&dst->lru);
+ migrate_folio_undo_dst(dst, true, put_new_page, private);
+
return rc;
}

@@ -1849,9 +1805,9 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,

__migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
migrate_folio_undo_src(folio, page_was_mapped, anon_vma,
- ret_folios);
+ true, ret_folios);
list_del(&dst->lru);
- migrate_folio_undo_dst(dst, put_new_page, private);
+ migrate_folio_undo_dst(dst, true, put_new_page, private);
dst = dst2;
dst2 = list_next_entry(dst, lru);
}
--
2.35.1