fs/pipe: unify the page pools into a single per-pipe pool

Pipes keep two separate page caches:
 a) The per-pipe, lock-protected tmp_page[2]
 b) An on-stack anon_pipe_prealloc burst pool of up to eight pages
    filled before the lock

Converge them into a single per-pipe pool (struct anon_pipe_prealloc
embedded in pipe_inode_info) with the same budget as before: up to
PIPE_PREALLOC_MAX (8) pages, trimmed back to PIPE_PREALLOC_KEEP (2)
after each operation. tmp_page[2] is removed.

Pages are still allocated and freed outside pipe->mutex; only the
assignment into the pool is done under it. The pool count is also read
locklessly in the prefill path, so it is annotated __data_racy.

anon_pipe_prefill_and_lock() tops the pool up to the write's page count
-- and returns with pipe->mutex held, so a write acquires the lock only
once.

anon_pipe_trim_and_unlock() trims the pool under that same lock before
dropping it, then frees the excess.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260720-b4-pipe-unification-v5-1-9002a3fe5e6d@debian.org
Reviewed-by: Mateusz Guzik <mjguzik@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions