mm: migration: factor out code to compute expected number of page references (0b3901b3) · Commits · 戴 / test

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:

Jan Kara <jack@suse.cz> Acked-by:

Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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;

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