On Sun, 24 May 2026 07:44:57 -0700, Breno Leitao wrote: > While profiling Meta's caching code[1], I found pipe->mutex contention > on the hot path. anon_pipe_write() currently calls alloc_page() once > per page while holding pipe->mutex. The allocation can sleep doing > direct reclaim and runs memcg charging, which extends the critical > section and stalls any concurrent reader on the same mutex. > > This series pre-allocates pages outside pipe->mutex in > anon_pipe_write(): for writes that span more than one full page, up > to PIPE_PREALLOC_MAX (8) pages are allocated via a per-page > alloc_page() loop before the mutex is taken. anon_pipe_get_page() > then drains the prealloc array first, falls back to the per-pipe > tmp_page[] cache, and only enters the allocator under the mutex for > the leftover pages (writes larger than PIPE_PREALLOC_MAX, single-page > writes that skip prealloc, or shortfalls when the prealloc loop > fails). Leftover prealloc pages are recycled into tmp_page[] before > unlock and any remainder is put_page()'d after unlock, keeping the > allocator out of the critical section on both sides. > > [...]
Applied to the vfs-7.2.misc branch of the vfs/vfs.git tree. Patches in the vfs-7.2.misc branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. Note that commit hashes shown below are subject to change due to rebase, trailer updates or similar. If in doubt, please check the listed branch. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs-7.2.misc [1/2] fs/pipe: pre-allocate pages outside pipe->mutex in anon_pipe_write https://git.kernel.org/vfs/vfs/c/212ed884a1ae [2/2] selftests/pipe: add pipe_bench microbenchmark https://git.kernel.org/vfs/vfs/c/d29bd8efe162
