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| author | David Sterba <dsterba@suse.com> | 2020-10-29 17:33:45 +0300 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2020-12-08 17:54:02 +0300 |
| commit | dc516164869300efd0bdbf6f894defc306588b75 (patch) | |
| tree | 670b5cc117f9622e06ee579310aca1be64e8be5b /fs/btrfs/extent_io.h | |
| parent | b9729ce014f6c22d4ca7fda97a7d8ea432af5f91 (diff) | |
| download | linux-dc516164869300efd0bdbf6f894defc306588b75.tar.xz | |
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 <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/extent_io.h')
| -rw-r--r-- | fs/btrfs/extent_io.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h index 5403354de0e1..3c2bf21c54eb 100644 --- a/fs/btrfs/extent_io.h +++ b/fs/btrfs/extent_io.h @@ -88,10 +88,10 @@ struct extent_buffer { struct rcu_head rcu_head; pid_t lock_owner; bool lock_recursed; - struct rw_semaphore lock; - /* >= 0 if eb belongs to a log tree, -1 otherwise */ - short log_index; + s8 log_index; + + struct rw_semaphore lock; struct page *pages[INLINE_EXTENT_BUFFER_PAGES]; #ifdef CONFIG_BTRFS_DEBUG |