6.8-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
commit 1db7959aacd905e6487d0478ac01d89f86eb1e51 upstream.
[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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/extent_io.c | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-)
--- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -692,31 +692,21 @@ static void end_bbio_data_read(struct bt 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; }