[PATCH 01/20] fs: Add aops->migrate_folio

Matthew Wilcox (Oracle)
2022-06-06T20:48:24Z

Provide a folio-based replacement for aops->migratepage. Update the
documentation to document migrate_folio instead of migratepage.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
Documentation/filesystems/locking.rst | 5 ++--
Documentation/filesystems/vfs.rst | 13 ++++++-----
Documentation/vm/page_migration.rst | 33 ++++++++++++++-------------
include/linux/fs.h | 4 +++-
mm/compaction.c | 4 +++-
mm/migrate.c | 19 ++++++++++-----
6 files changed, 46 insertions(+), 32 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index c0fe711f14d3..3d28b23676bd 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -253,7 +253,8 @@ prototypes::
void (*free_folio)(struct folio *);
int (*direct_IO)(struct kiocb *, struct iov_iter *iter);
bool (*isolate_page) (struct page *, isolate_mode_t);
- int (*migratepage)(struct address_space *, struct page *, struct page *);
+ int (*migrate_folio)(struct address_space *, struct folio *dst,
+ struct folio *src, enum migrate_mode);
void (*putback_page) (struct page *);
int (*launder_folio)(struct folio *);
bool (*is_partially_uptodate)(struct folio *, size_t from, size_t count);
@@ -281,7 +282,7 @@ release_folio: yes
free_folio: yes
direct_IO:
isolate_page: yes
-migratepage: yes (both)
+migrate_folio: yes (both)
putback_page: yes
launder_folio: yes
is_partially_uptodate: yes
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index a08c652467d7..3ae1b039b03f 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -740,7 +740,8 @@ cache in your filesystem. The following members are defined:
/* isolate a page for migration */
bool (*isolate_page) (struct page *, isolate_mode_t);
/* migrate the contents of a page to the specified target */
- int (*migratepage) (struct page *, struct page *);
+ int (*migrate_folio)(struct mapping *, struct folio *dst,
+ struct folio *src, enum migrate_mode);
/* put migration-failed page back to right list */
void (*putback_page) (struct page *);
int (*launder_folio) (struct folio *);
@@ -935,12 +936,12 @@ cache in your filesystem. The following members are defined:
is successfully isolated, VM marks the page as PG_isolated via
__SetPageIsolated.

-``migrate_page``
+``migrate_folio``
This is used to compact the physical memory usage. If the VM
- wants to relocate a page (maybe off a memory card that is
- signalling imminent failure) it will pass a new page and an old
- page to this function. migrate_page should transfer any private
- data across and update any references that it has to the page.
+ wants to relocate a folio (maybe from a memory device that is
+ signalling imminent failure) it will pass a new folio and an old
+ folio to this function. migrate_folio should transfer any private
+ data across and update any references that it has to the folio.

``putback_page``
Called by the VM when isolated page's migration fails.
diff --git a/Documentation/vm/page_migration.rst b/Documentation/vm/page_migration.rst
index 8c5cb8147e55..e0f73ddfabb1 100644
--- a/Documentation/vm/page_migration.rst
+++ b/Documentation/vm/page_migration.rst
@@ -181,22 +181,23 @@ which are function pointers of struct address_space_operations.
Once page is successfully isolated, VM uses page.lru fields so driver
shouldn't expect to preserve values in those fields.

-2. ``int (*migratepage) (struct address_space *mapping,``
-| ``struct page *newpage, struct page *oldpage, enum migrate_mode);``
-
- After isolation, VM calls migratepage() of driver with the isolated page.
- The function of migratepage() is to move the contents of the old page to the
- new page
- and set up fields of struct page newpage. Keep in mind that you should
- indicate to the VM the oldpage is no longer movable via __ClearPageMovable()
- under page_lock if you migrated the oldpage successfully and returned
- MIGRATEPAGE_SUCCESS. If driver cannot migrate the page at the moment, driver
- can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time
- because VM interprets -EAGAIN as "temporary migration failure". On returning
- any error except -EAGAIN, VM will give up the page migration without
- retrying.
-
- Driver shouldn't touch the page.lru field while in the migratepage() function.
+2. ``int (*migrate_folio) (struct address_space *mapping,``
+| ``struct folio *dst, struct folio *src, enum migrate_mode);``
+
+ After isolation, VM calls the driver's migrate_folio() with the
+ isolated folio. The purpose of migrate_folio() is to move the contents
+ of the source folio to the destination folio and set up the fields
+ of destination folio. Keep in mind that you should indicate to the
+ VM the source folio is no longer movable via __ClearPageMovable()
+ under folio if you migrated the source successfully and returned
+ MIGRATEPAGE_SUCCESS. If driver cannot migrate the folio at the
+ moment, driver can return -EAGAIN. On -EAGAIN, VM will retry folio
+ migration in a short time because VM interprets -EAGAIN as "temporary
+ migration failure". On returning any error except -EAGAIN, VM will
+ give up the folio migration without retrying.
+
+ Driver shouldn't touch the folio.lru field while in the migrate_folio()
+ function.

3. ``void (*putback_page)(struct page *);``

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9ad5e3520fae..7b380fa66983 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -362,9 +362,11 @@ struct address_space_operations {
void (*free_folio)(struct folio *folio);
ssize_t (*direct_IO)(struct kiocb *, struct iov_iter *iter);
/*
- * migrate the contents of a page to the specified target. If
+ * migrate the contents of a folio to the specified target. If
* migrate_mode is MIGRATE_ASYNC, it must not block.
*/
+ int (*migrate_folio)(struct address_space *, struct folio *dst,
+ struct folio *src, enum migrate_mode);
int (*migratepage) (struct address_space *,
struct page *, struct page *, enum migrate_mode);
bool (*isolate_page)(struct page *, isolate_mode_t);
diff --git a/mm/compaction.c b/mm/compaction.c
index 1f89b969c12b..db34b459e5d9 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1045,7 +1045,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
goto isolate_fail_put;

mapping = page_mapping(page);
- migrate_dirty = !mapping || mapping->a_ops->migratepage;
+ migrate_dirty = !mapping ||
+ mapping->a_ops->migrate_folio ||
+ mapping->a_ops->migratepage;
unlock_page(page);
if (!migrate_dirty)
goto isolate_fail_put;
diff --git a/mm/migrate.c b/mm/migrate.c
index e51588e95f57..75cb6aa38988 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -858,14 +858,17 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
if (likely(is_lru)) {
if (!mapping)
rc = migrate_page(mapping, &dst->page, &src->page, mode);
- else if (mapping->a_ops->migratepage)
+ else if (mapping->a_ops->migrate_folio)
/*
- * Most pages have a mapping and most filesystems
- * provide a migratepage callback. Anonymous pages
+ * 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
- * migratepage callback. This is the most common path
+ * migrate_folio callback. This is the most common path
* for page migration.
*/
+ rc = mapping->a_ops->migrate_folio(mapping, dst, src,
+ mode);
+ else if (mapping->a_ops->migratepage)
rc = mapping->a_ops->migratepage(mapping, &dst->page,
&src->page, mode);
else
@@ -883,8 +886,12 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
goto out;
}

- rc = mapping->a_ops->migratepage(mapping, &dst->page,
- &src->page, mode);
+ if (mapping->a_ops->migrate_folio)
+ rc = mapping->a_ops->migrate_folio(mapping, dst, src,
+ mode);
+ else
+ rc = mapping->a_ops->migratepage(mapping, &dst->page,
+ &src->page, mode);
WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
!folio_test_isolated(src));
}
--
2.35.1