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Commit 0b3901b3 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
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mm: migration: factor out code to compute expected number of page references 

Patch series "mm: migrate: Fix page migration stalls for blkdev pages".

This patchset deals with page migration stalls that were reported by our
customer due to a block device page that had a bufferhead that was in the
bh LRU cache.

The patchset modifies the page migration code so that bufferheads are
completely handled inside buffer_migrate_page() and then provides a new
migration helper for pages with buffer heads that is safe to use even for
block device pages and that also deals with bh lrus.

This patch (of 6):

Factor out function to compute number of expected page references in
migrate_page_move_mapping().  Note that we move hpage_nr_pages() and
page_has_private() checks from under xas_lock_irq() however this is safe
since we hold page lock.

[jack@suse.cz: fix expected_page_refs()]
  Link: http://lkml.kernel.org/r/20181217131710.GB8611@quack2.suse.cz
Link: http://lkml.kernel.org/r/20181211172143.7358-2-jack@suse.cz


Signed-off-by: default avatarJan Kara <jack@suse.cz>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d9367bd0

mm/migrate.c

+17 −10
Original line number Diff line number Diff line
@@ -424,6 +424,22 @@ static inline bool buffer_migrate_lock_buffers(struct buffer_head *head, 
}

#endif /* CONFIG_BLOCK */



static int expected_page_refs(struct page *page)

{

	int expected_count = 1;



	/*

	 * Device public or private pages have an extra refcount as they are

	 * ZONE_DEVICE pages.

	 */

	expected_count += is_device_private_page(page);

	expected_count += is_device_public_page(page);

	if (page_mapping(page))

		expected_count += hpage_nr_pages(page) + page_has_private(page);



	return expected_count;

}



/*

 * Replace the page in the mapping.

 *
@@ -440,14 +456,7 @@ int migrate_page_move_mapping(struct address_space *mapping, 
	XA_STATE(xas, &mapping->i_pages, page_index(page));

	struct zone *oldzone, *newzone;

	int dirty;

	int expected_count = 1 + extra_count;



	/*

	 * Device public or private pages have an extra refcount as they are

	 * ZONE_DEVICE pages.

	 */

	expected_count += is_device_private_page(page);

	expected_count += is_device_public_page(page);

	int expected_count = expected_page_refs(page) + extra_count;



	if (!mapping) {

		/* Anonymous page without mapping */
@@ -467,8 +476,6 @@ int migrate_page_move_mapping(struct address_space *mapping, 
	newzone = page_zone(newpage);



	xas_lock_irq(&xas);



	expected_count += hpage_nr_pages(page) + page_has_private(page);

	if (page_count(page) != expected_count || xas_load(&xas) != page) {

		xas_unlock_irq(&xas);

		return -EAGAIN;