Btrfs: change reserved_extents to an atomic_t
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>
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index ccc991c..57c3bb2 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -136,9 +136,8 @@
* items we think we'll end up using, and reserved_extents is the number
* of extent items we've reserved metadata for.
*/
- spinlock_t accounting_lock;
atomic_t outstanding_extents;
- int reserved_extents;
+ atomic_t reserved_extents;
/*
* ordered_data_close is set by truncate when a file that used
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7b3089b..27376c9 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3996,6 +3996,7 @@
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 @@
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 @@
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)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 9007bbd..d97b69a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6632,9 +6632,8 @@
ei->index_cnt = (u64)-1;
ei->last_unlink_trans = 0;
- spin_lock_init(&ei->accounting_lock);
atomic_set(&ei->outstanding_extents, 0);
- ei->reserved_extents = 0;
+ atomic_set(&ei->reserved_extents, 0);
ei->ordered_data_close = 0;
ei->orphan_meta_reserved = 0;
@@ -6670,7 +6669,7 @@
WARN_ON(!list_empty(&inode->i_dentry));
WARN_ON(inode->i_data.nrpages);
WARN_ON(atomic_read(&BTRFS_I(inode)->outstanding_extents));
- WARN_ON(BTRFS_I(inode)->reserved_extents);
+ WARN_ON(atomic_read(&BTRFS_I(inode)->reserved_extents));
/*
* This can happen where we create an inode, but somebody else also