[PATCH v7 0/2] mm, netfs, fscache: Stop read optimisation when folio removed from pagecache

[David Howells]

Hi Andrew,

Should this go through the mm tree?

This fixes an optimisation in fscache whereby we don't read from the cache
for a particular file until we know that there's data there that we don't
have in the pagecache.  The problem is that I'm no longer using PG_fscache
(aka PG_private_2) to indicate that the page is cached and so I don't get a
notification when a cached page is dropped from the pagecache.

The first patch merges some folio_has_private() and filemap_release_folio()
pairs and introduces a helper, folio_needs_release(), to indicate if a
release is required.

The second patch is the actual fix.  Following Willy's suggestions[1], it
adds an AS_RELEASE_ALWAYS flag to an address_space that will make
filemap_release_folio() always call ->release_folio(), even if
PG_private/PG_private_2 aren't set.  folio_needs_release() is altered to
add a check for this.

David

Changes:
========
ver #7)
 - Make NFS set AS_RELEASE_ALWAYS.

ver #6)
 - Drop the third patch which removes a duplicate check in vmscan().

ver #5)
 - Rebased on linus/master.  try_to_release_page() has now been entirely
   replaced by filemap_release_folio(), barring one comment.
 - Cleaned up some pairs in ext4.

ver #4)
 - Split has_private/release call pairs into own patch.
 - Moved folio_needs_release() to mm/internal.h and removed open-coded
   version from filemap_release_folio().
 - Don't need to clear AS_RELEASE_ALWAYS in ->evict_inode().
 - Added experimental patch to reduce shrink_folio_list().

ver #3)
 - Fixed mapping_clear_release_always() to use clear_bit() not set_bit().
 - Moved a '&&' to the correct line.

ver #2)
 - Rewrote entirely according to Willy's suggestion[1].

Link: https://lore.kernel.org/r/Yk9V/03wgdYi65Lb@casper.infradead.org/ [1]
Link: https://lore.kernel.org/r/164928630577.457102.8519251179327601178.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/166844174069.1124521.10890506360974169994.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/166869495238.3720468.4878151409085146764.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/1459152.1669208550@warthog.procyon.org.uk/ # v3 also
Link: https://lore.kernel.org/r/166924370539.1772793.13730698360771821317.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/167172131368.2334525.8569808925687731937.stgit@warthog.procyon.org.uk/ # v5
Link: https://lore.kernel.org/r/20230216150701.3654894-1-dhowells@redhat.com/ # v6

David Howells (2):
  mm: Merge folio_has_private()/filemap_release_folio() call pairs
  mm, netfs, fscache: Stop read optimisation when folio removed from
    pagecache

 fs/9p/cache.c           |  2 ++
 fs/afs/internal.h       |  2 ++
 fs/cachefiles/namei.c   |  2 ++
 fs/ceph/cache.c         |  2 ++
 fs/ext4/move_extent.c   | 12 ++++--------
 fs/nfs/fscache.c        |  3 +++
 fs/smb/client/fscache.c |  2 ++
 fs/splice.c             |  3 +--
 include/linux/pagemap.h | 16 ++++++++++++++++
 mm/filemap.c            |  2 ++
 mm/huge_memory.c        |  3 +--
 mm/internal.h           | 11 +++++++++++
 mm/khugepaged.c         |  3 +--
 mm/memory-failure.c     |  8 +++-----
 mm/migrate.c            |  3 +--
 mm/truncate.c           |  6 ++----
 mm/vmscan.c             |  8 ++++----
 17 files changed, 59 insertions(+), 29 deletions(-)