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btrfs: accessors: compile-time fast path for u8

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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>
This commit is contained in:
David Sterba 2025-07-01 19:23:51 +02:00
parent d5a87dbd95
commit 58383c6866
1 changed files with 3 additions and 2 deletions
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5
fs/btrfs/accessors.c
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@ -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; \