diff options
| author | David Sterba <[email protected]> | 2020-10-29 15:33:45 +0100 |
|---|---|---|
| committer | David Sterba <[email protected]> | 2020-12-08 15:54:02 +0100 |
| commit | dc516164869300efd0bdbf6f894defc306588b75 (patch) | |
| tree | 670b5cc117f9622e06ee579310aca1be64e8be5b /lib/test_overflow.c | |
| parent | b9729ce014f6c22d4ca7fda97a7d8ea432af5f91 (diff) | |
btrfs: reorder extent buffer members for better packing
After the rwsem replaced the tree lock implementation, the extent buffer
got smaller but leaving some holes behind. By changing log_index type
and reordering, we can squeeze the size further to 240 bytes, measured on
release config on x86_64. Log_index spans only 3 values and needs to be
signed.
Before:
struct extent_buffer {
u64 start; /* 0 8 */
long unsigned int len; /* 8 8 */
long unsigned int bflags; /* 16 8 */
struct btrfs_fs_info * fs_info; /* 24 8 */
spinlock_t refs_lock; /* 32 4 */
atomic_t refs; /* 36 4 */
atomic_t io_pages; /* 40 4 */
int read_mirror; /* 44 4 */
struct callback_head callback_head __attribute__((__aligned__(8))); /* 48 16 */
/* --- cacheline 1 boundary (64 bytes) --- */
pid_t lock_owner; /* 64 4 */
bool lock_recursed; /* 68 1 */
/* XXX 3 bytes hole, try to pack */
struct rw_semaphore lock; /* 72 40 */
short int log_index; /* 112 2 */
/* XXX 6 bytes hole, try to pack */
struct page * pages[16]; /* 120 128 */
/* size: 248, cachelines: 4, members: 14 */
/* sum members: 239, holes: 2, sum holes: 9 */
/* forced alignments: 1 */
/* last cacheline: 56 bytes */
} __attribute__((__aligned__(8)));
After:
struct extent_buffer {
u64 start; /* 0 8 */
long unsigned int len; /* 8 8 */
long unsigned int bflags; /* 16 8 */
struct btrfs_fs_info * fs_info; /* 24 8 */
spinlock_t refs_lock; /* 32 4 */
atomic_t refs; /* 36 4 */
atomic_t io_pages; /* 40 4 */
int read_mirror; /* 44 4 */
struct callback_head callback_head __attribute__((__aligned__(8))); /* 48 16 */
/* --- cacheline 1 boundary (64 bytes) --- */
pid_t lock_owner; /* 64 4 */
bool lock_recursed; /* 68 1 */
s8 log_index; /* 69 1 */
/* XXX 2 bytes hole, try to pack */
struct rw_semaphore lock; /* 72 40 */
struct page * pages[16]; /* 112 128 */
/* size: 240, cachelines: 4, members: 14 */
/* sum members: 238, holes: 1, sum holes: 2 */
/* forced alignments: 1 */
/* last cacheline: 48 bytes */
} __attribute__((__aligned__(8)));
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: David Sterba <[email protected]>
Diffstat (limited to 'lib/test_overflow.c')
0 files changed, 0 insertions, 0 deletions