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Btrfs: change reserved_extents to an atomic_t

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We track delayed allocation per inodes via 2 counters, one is
outstanding_extents and reserved_extents.  Outstanding_extents is already an
atomic_t, but reserved_extents is not and is protected by a spinlock.  So
convert this to an atomic_t and instead of using a spinlock, use atomic_cmpxchg
when releasing delalloc bytes.  This makes our inode 72 bytes smaller, and
reduces locking overhead (albiet it was minimal to begin with).  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
This commit is contained in:
Josef Bacik
2011-01-25 16:30:38 -05:00
parent 4a64001f00
commit 57a45ced94
3 changed files with 29 additions and 21 deletions
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42
fs/btrfs/extent-tree.c
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@@ -3996,6 +3996,7 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
struct btrfs_block_rsv *block_rsv = &root->fs_info->delalloc_block_rsv;
u64 to_reserve;
int nr_extents;
int reserved_extents;
int ret;
if (btrfs_transaction_in_commit(root->fs_info))
@@ -4003,25 +4004,24 @@ int btrfs_delalloc_reserve_metadata(struct inode *inode, u64 num_bytes)
num_bytes = ALIGN(num_bytes, root->sectorsize);
spin_lock(&BTRFS_I(inode)->accounting_lock);
nr_extents = atomic_read(&BTRFS_I(inode)->outstanding_extents) + 1;
if (nr_extents > BTRFS_I(inode)->reserved_extents) {
nr_extents -= BTRFS_I(inode)->reserved_extents;
reserved_extents = atomic_read(&BTRFS_I(inode)->reserved_extents);
if (nr_extents > reserved_extents) {
nr_extents -= reserved_extents;
to_reserve = calc_trans_metadata_size(root, nr_extents);
} else {
nr_extents = 0;
to_reserve = 0;
}
spin_unlock(&BTRFS_I(inode)->accounting_lock);
to_reserve += calc_csum_metadata_size(inode, num_bytes);
ret = reserve_metadata_bytes(NULL, root, block_rsv, to_reserve, 1);
if (ret)
return ret;
spin_lock(&BTRFS_I(inode)->accounting_lock);
BTRFS_I(inode)->reserved_extents += nr_extents;
atomic_add(nr_extents, &BTRFS_I(inode)->reserved_extents);
atomic_inc(&BTRFS_I(inode)->outstanding_extents);
spin_unlock(&BTRFS_I(inode)->accounting_lock);
block_rsv_add_bytes(block_rsv, to_reserve, 1);
@@ -4036,20 +4036,30 @@ void btrfs_delalloc_release_metadata(struct inode *inode, u64 num_bytes)
struct btrfs_root *root = BTRFS_I(inode)->root;
u64 to_free;
int nr_extents;
int reserved_extents;
num_bytes = ALIGN(num_bytes, root->sectorsize);
atomic_dec(&BTRFS_I(inode)->outstanding_extents);
WARN_ON(atomic_read(&BTRFS_I(inode)->outstanding_extents) < 0);
spin_lock(&BTRFS_I(inode)->accounting_lock);
nr_extents = atomic_read(&BTRFS_I(inode)->outstanding_extents);
if (nr_extents < BTRFS_I(inode)->reserved_extents) {
nr_extents = BTRFS_I(inode)->reserved_extents - nr_extents;
BTRFS_I(inode)->reserved_extents -= nr_extents;
} else {
nr_extents = 0;
}
spin_unlock(&BTRFS_I(inode)->accounting_lock);
reserved_extents = atomic_read(&BTRFS_I(inode)->reserved_extents);
do {
int old, new;
nr_extents = atomic_read(&BTRFS_I(inode)->outstanding_extents);
if (nr_extents >= reserved_extents) {
nr_extents = 0;
break;
}
old = reserved_extents;
nr_extents = reserved_extents - nr_extents;
new = reserved_extents - nr_extents;
old = atomic_cmpxchg(&BTRFS_I(inode)->reserved_extents,
reserved_extents, new);
if (likely(old == reserved_extents))
break;
reserved_extents = old;
} while (1);
to_free = calc_csum_metadata_size(inode, num_bytes);
if (nr_extents > 0)