btrfs: accessors: compile-time fast path for u8

Reading/writing 1 byte (u8) is a special case compared to the others as
it's always contained in the folio we find, so the split memcpy will
never be needed. Turn it to a compile-time check that the memcpy part
can be optimized out.

The stack usage is reduced:

  btrfs_set_8                                         -16 (32 -> 16)
  btrfs_get_8                                         -16 (24 -> 8)

Code size reduction:

     text    data     bss     dec     hex filename
  1454951  115665   16088 1586704  183610 pre/btrfs.ko
  1454691  115665   16088 1586444  18350c post/btrfs.ko

  DELTA: -260

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/accessors.c b/fs/btrfs/accessors.c
index a7b6b2d7bde224e02d66de3078085a42c9e5084e..547e9f8fb87d619c63164ae185953d3a3f691dcb 100644 (file)
--- a/fs/btrfs/accessors.c
+++ b/fs/btrfs/accessors.c
@@ -55,7 +55,8 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb,              \
                report_setget_bounds(eb, ptr, off, sizeof(u##bits));    \
                return 0;                                               \
        }                                                               \
-       if (INLINE_EXTENT_BUFFER_PAGES == 1 || likely(sizeof(u##bits) <= part)) \
+       if (INLINE_EXTENT_BUFFER_PAGES == 1 || sizeof(u##bits) == 1 ||  \
+           likely(sizeof(u##bits) <= part))                            \
                return get_unaligned_le##bits(kaddr + oil);             \
                                                                        \
        memcpy(lebytes, kaddr + oil, part);                             \
@@ -78,7 +79,7 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr,      \
                report_setget_bounds(eb, ptr, off, sizeof(u##bits));    \
                return;                                                 \
        }                                                               \
-       if (INLINE_EXTENT_BUFFER_PAGES == 1 ||                          \
+       if (INLINE_EXTENT_BUFFER_PAGES == 1 || sizeof(u##bits) == 1 ||  \
            likely(sizeof(u##bits) <= part)) {                          \
                put_unaligned_le##bits(val, kaddr + oil);               \
                return;                                                 \