[PATCH 2/7] btrfs: accessors: use type sizeof constants directly

David Sterba
2025-07-01T17:24:06Z

Now unit_size is used only once, so use it directly in 'part'
calculation. Don't cache sizeof(type) in a variable. While this is a
compile-time constant, forcing the type 'int' generates worse code as it
leads to additional conversion from 32 to 64 bit type on x86_64.

The sizeof() is used only a few times and it does not make the code that
harder to read, so use it directly and let the compiler utilize the
immediate constants in the context it needs. The .ko code size slightly
increases (+50) but further patches will reduce that again.

Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/accessors.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/accessors.c b/fs/btrfs/accessors.c
index b54c8abe467a06..2e90b9b14e73f4 100644
--- a/fs/btrfs/accessors.c
+++ b/fs/btrfs/accessors.c
@@ -52,19 +52,17 @@ u##bits btrfs_get_##bits(const struct extent_buffer *eb, \
const unsigned long idx = get_eb_folio_index(eb, member_offset);\
const unsigned long oil = get_eb_offset_in_folio(eb, \
member_offset);\
- const int unit_size = eb->folio_size; \
char *kaddr = folio_address(eb->folios[idx]); \
- const int size = sizeof(u##bits); \
- const int part = unit_size - oil; \
+ const int part = eb->folio_size - oil; \
u8 lebytes[sizeof(u##bits)]; \
\
- ASSERT(check_setget_bounds(eb, ptr, off, size)); \
+ ASSERT(check_setget_bounds(eb, ptr, off, sizeof(u##bits))); \
if (INLINE_EXTENT_BUFFER_PAGES == 1 || likely(sizeof(u##bits) <= part)) \
return get_unaligned_le##bits(kaddr + oil); \
\
memcpy(lebytes, kaddr + oil, part); \
kaddr = folio_address(eb->folios[idx + 1]); \
- memcpy(lebytes + part, kaddr, size - part); \
+ memcpy(lebytes + part, kaddr, sizeof(u##bits) - part); \
return get_unaligned_le##bits(lebytes); \
} \
void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
@@ -74,13 +72,11 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
const unsigned long idx = get_eb_folio_index(eb, member_offset);\
const unsigned long oil = get_eb_offset_in_folio(eb, \
member_offset);\
- const int unit_size = eb->folio_size; \
char *kaddr = folio_address(eb->folios[idx]); \
- const int size = sizeof(u##bits); \
- const int part = unit_size - oil; \
+ const int part = eb->folio_size - oil; \
u8 lebytes[sizeof(u##bits)]; \
\
- ASSERT(check_setget_bounds(eb, ptr, off, size)); \
+ ASSERT(check_setget_bounds(eb, ptr, off, sizeof(u##bits))); \
if (INLINE_EXTENT_BUFFER_PAGES == 1 || \
likely(sizeof(u##bits) <= part)) { \
put_unaligned_le##bits(val, kaddr + oil); \
@@ -90,7 +86,7 @@ void btrfs_set_##bits(const struct extent_buffer *eb, void *ptr, \
put_unaligned_le##bits(val, lebytes); \
memcpy(kaddr + oil, lebytes, part); \
kaddr = folio_address(eb->folios[idx + 1]); \
- memcpy(kaddr, lebytes + part, size - part); \
+ memcpy(kaddr, lebytes + part, sizeof(u##bits) - part); \
}

DEFINE_BTRFS_SETGET_BITS(8)
--
2.49.0