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Date:   Wed,  8 Jun 2022 16:02:33 +0100
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-aio@...ck.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel@...hat.com, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net, ocfs2-devel@....oracle.com,
        linux-mtd@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v2 03/19] fs: Add aops->migrate_folio

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@...radead.org>
Reviewed-by: Christoph Hellwig <hch@....de>
---
 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                          | 11 +++++----
 6 files changed, 40 insertions(+), 30 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 5d8ee3155ca2..47431cf8fbb3 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);
 	int (*launder_folio)(struct folio *);
diff --git a/mm/compaction.c b/mm/compaction.c
index f23efba1d118..458f49f9ab09 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1042,7 +1042,9 @@ 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 3ce6fee87efa..e064b998ead0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -856,14 +856,17 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
 
 		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
-- 
2.35.1

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