A page containing buffer_heads can be pinned if any of its constituent buffer_heads belongs to the BH LRU cache [1], which can prevent that page from being migrated. 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]. V2: Respond to feedback provided by Andrew, Minchan and Matthew in [3]. As suggested by Minchan, we're now doing the invalidate of the LRUs in a fashion similar to how the pagevecs are drained in lru_add_drain_all() [1] https://elixir.bootlin.com/linux/latest/source/fs/buffer.c#L1238 [2] https://lore.kernel.org/linux-fsdevel/cover.1611642038.git.cgoldswo@xxxxxxxxxxxxxx/ [3] https://lkml.org/lkml/2021/2/2/68 Chris Goldsworthy (1): [RFC] mm: fs: Invalidate BH LRU during page migration fs/buffer.c | 54 +++++++++++++++++++++++++++++++++++++++++++-- include/linux/buffer_head.h | 8 +++++++ include/linux/migrate.h | 2 ++ mm/migrate.c | 19 ++++++++++++++++ mm/page_alloc.c | 3 +++ mm/swap.c | 7 +++++- 6 files changed, 90 insertions(+), 3 deletions(-) -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
