[PATCH v2] [RFC] Invalidate BH LRU during page migration

[Chris Goldsworthy <cgoldswo@codeaurora.org>]

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@codeaurora.org/
[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(-)

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