From: Jan Kara <jack@xxxxxxx> Subject: 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@xxxxxxx: fix expected_page_refs()] Link: http://lkml.kernel.org/r/20181217131710.GB8611@xxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20181211172143.7358-2-jack@xxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/mm/migrate.c~mm-migration-factor-out-code-to-compute-expected-number-of-page-references +++ a/mm/migrate.c @@ -424,6 +424,22 @@ static inline bool buffer_migrate_lock_b } #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 add 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 add 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; _
