improve pagecache PSI annotations v2

[Christoph Hellwig]

Hi all,

currently the VM tries to abuse the block layer submission path for
the page cache PSI annotations.  This series instead annotates the
->read_folio and ->readahead calls in the core VM code, and then
only deals with the odd direct add_to_page_cache_lru calls manually.

Changes since v1:
 - fix a logic error in ra_alloc_folio
 - drop a unlikely()
 - spell a comment in the weird way preferred by btrfs maintainers

Diffstat:
 block/bio.c               |    8 --------
 block/blk-core.c          |   17 -----------------
 fs/btrfs/compression.c    |   14 ++++++++++++--
 fs/direct-io.c            |    2 --
 fs/erofs/zdata.c          |   13 ++++++++++++-
 include/linux/blk_types.h |    1 -
 include/linux/pagemap.h   |    2 ++
 kernel/sched/psi.c        |    2 ++
 mm/filemap.c              |    7 +++++++
 mm/readahead.c            |   22 ++++++++++++++++++----
 10 files changed, 53 insertions(+), 35 deletions(-)