From 00c0cf844465139ee6d9b271549295da3c7822ca Mon Sep 17 00:00:00 2001 From: David Sterba Date: Tue, 1 Jul 2025 19:23:48 +0200 Subject: [PATCH] btrfs: accessors: simplify folio bounds checks As we can a have non-contiguous range in the eb->folios, any item can be straddling two folios and we need to check if it can be read in one go or in two parts. For that there's a check which is not implemented in the simplest way: offset in folio + size <= folio size With a simple expression transformation: oil + size <= unit_size size <= unit_size - oil sizeof() <= part this can be simplified and reusing existing run-time or compile-time constants. Add likely() annotation for this expression as this is the fast path and compiler sometimes reorders that after the followup block with the memcpy (observed in practice with other simplifications). Overall effect on stack consumption: btrfs_get_8 -8 (80 -> 72) btrfs_set_8 -8 (88 -> 80) And .ko size (due to optimizations making use of the direct constants): text data bss dec hex filename 1456601 115665 16088 1588354 183c82 pre/btrfs.ko 1456093 115665 16088 1587846 183a86 post/btrfs.ko DELTA: -508 Reviewed-by: Boris Burkov Signed-off-by: David Sterba --- fs/btrfs/accessors.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/accessors.c b/fs/btrfs/accessors.c index 5cfb0801700e6..b54c8abe467a0 100644 --- a/fs/btrfs/accessors.c +++ b/fs/btrfs/accessors.c @@ -59,7 +59,7 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb, \ u8 lebytes[sizeof(u##bits)]; \ \ ASSERT(check_setget_bounds(eb, ptr, off, size)); \ - if (INLINE_EXTENT_BUFFER_PAGES == 1 || oil + size <= unit_size) \ + if (INLINE_EXTENT_BUFFER_PAGES == 1 || likely(sizeof(u##bits) <= part)) \ return get_unaligned_le##bits(kaddr + oil); \ \ memcpy(lebytes, kaddr + oil, part); \ @@ -82,7 +82,7 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \ \ ASSERT(check_setget_bounds(eb, ptr, off, size)); \ if (INLINE_EXTENT_BUFFER_PAGES == 1 || \ - oil + size <= unit_size) { \ + likely(sizeof(u##bits) <= part)) { \ put_unaligned_le##bits(val, kaddr + oil); \ return; \ } \ -- 2.47.2