The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 1db7959aacd905e6487d0478ac01d89f86eb1e51 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024041951-sports-hula-f2a5@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

1db7959aacd9 ("btrfs: do not wait for short bulk allocation") 09e6cef19c9f ("btrfs: refactor alloc_extent_buffer() to allocate-then-attach method") 397239ed6a6c ("btrfs: allow extent buffer helpers to skip cross-page handling") 94dbf7c0871f ("btrfs: free the allocated memory if btrfs_alloc_page_array() fails")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1db7959aacd905e6487d0478ac01d89f86eb1e51 Mon Sep 17 00:00:00 2001 From: Qu Wenruo wqu@suse.com Date: Tue, 26 Mar 2024 09:16:46 +1030 Subject: [PATCH] btrfs: do not wait for short bulk allocation

[BUG] There is a recent report that when memory pressure is high (including cached pages), btrfs can spend most of its time on memory allocation in btrfs_alloc_page_array() for compressed read/write.

[CAUSE] For btrfs_alloc_page_array() we always go alloc_pages_bulk_array(), and even if the bulk allocation failed (fell back to single page allocation) we still retry but with extra memalloc_retry_wait().

If the bulk alloc only returned one page a time, we would spend a lot of time on the retry wait.

The behavior was introduced in commit 395cb57e8560 ("btrfs: wait between incomplete batch memory allocations").

[FIX] Although the commit mentioned that other filesystems do the wait, it's not the case at least nowadays.

All the mainlined filesystems only call memalloc_retry_wait() if they failed to allocate any page (not only for bulk allocation). If there is any progress, they won't call memalloc_retry_wait() at all.

For example, xfs_buf_alloc_pages() would only call memalloc_retry_wait() if there is no allocation progress at all, and the call is not for metadata readahead.

So I don't believe we should call memalloc_retry_wait() unconditionally for short allocation.

Call memalloc_retry_wait() if it fails to allocate any page for tree block allocation (which goes with __GFP_NOFAIL and may not need the special handling anyway), and reduce the latency for btrfs_alloc_page_array().

Reported-by: Julian Taylor julian.taylor@1und1.de Tested-by: Julian Taylor julian.taylor@1und1.de Link: https://lore.kernel.org/all/8966c095-cbe7-4d22-9784-a647d1bf27c3@1und1.de/ Fixes: 395cb57e8560 ("btrfs: wait between incomplete batch memory allocations") CC: stable@vger.kernel.org # 6.1+ Reviewed-by: Sweet Tea Dorminy sweettea-kernel@dorminy.me Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index b18034f2ab80..2776112dbdf8 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -681,31 +681,21 @@ static void end_bbio_data_read(struct btrfs_bio *bbio) int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array, gfp_t extra_gfp) { + const gfp_t gfp = GFP_NOFS | extra_gfp; unsigned int allocated;

for (allocated = 0; allocated < nr_pages;) { unsigned int last = allocated;

- allocated = alloc_pages_bulk_array(GFP_NOFS | extra_gfp, - nr_pages, page_array); - - if (allocated == nr_pages) - return 0; - - /* - * During this iteration, no page could be allocated, even - * though alloc_pages_bulk_array() falls back to alloc_page() - * if it could not bulk-allocate. So we must be out of memory. - */ - if (allocated == last) { + allocated = alloc_pages_bulk_array(gfp, nr_pages, page_array); + if (unlikely(allocated == last)) { + /* No progress, fail and do cleanup. */ for (int i = 0; i < allocated; i++) { __free_page(page_array[i]); page_array[i] = NULL; } return -ENOMEM; } - - memalloc_retry_wait(GFP_NOFS); } return 0; }