A page containing buffer_heads can be pinned if any of its constituent buffer_heads belongs to the BH LRU cache [1]. After going through several iterations of a patch that attempts to solve this by removing BH entries inside of the drop_buffers() function, which in the worst-case could be called for each migrated page, Minchan Kim suggested that we invalidate the entire BH LRU once, just before we start migrating pages. Additionally, Matthew Wilcox suggested that we invalidate the BH LRU inside of lru_add_drain_all(), so as to benefit functions like other functions that would be impacted by pinned pages [2]. TODO: - It should be possible to remove the initial setting of bh_migration_done = false; in migrate_prep by passing this in as a parameter to invalidate_bh_lru(), but we'd still need a matching bh_migration_done = true; call. - To really benefit other callers of lru_add_drain_all() other than __alloc_contig_migrate_range() in the CMA allocaiton path, we'd need to add additional calls of bh_migration_done = false; [1] https://elixir.bootlin.com/linux/latest/source/fs/buffer.c#L1238 [2] https://lore.kernel.org/linux-fsdevel/cover.1611642038.git.cgoldswo@xxxxxxxxxxxxxx/ Chris Goldsworthy (1): [RFC] mm: fs: Invalidate BH LRU during page migration fs/buffer.c | 6 ++++++ include/linux/buffer_head.h | 3 +++ include/linux/migrate.h | 2 ++ mm/migrate.c | 18 ++++++++++++++++++ mm/page_alloc.c | 3 +++ mm/swap.c | 3 +++ 6 files changed, 35 insertions(+) -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
