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Btrfs: make fsync latency less sucky

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Looking into some performance related issues with large amounts of metadata
revealed that we can have some pretty huge swings in fsync() performance.  If we
have a lot of delayed refs backed up (as you will tend to do with lots of
metadata) fsync() will wander off and try to run some of those delayed refs
which can result in reading from disk and such.  Since the actual act of fsync()
doesn't create any delayed refs there is no need to make it throttle on delayed
ref stuff, that will be handled by other people.  With this patch we get much
smoother fsync performance with large amounts of metadata.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Josef Bacik
2014-01-15 13:34:13 -05:00
committed by Chris Mason
parent 63541927c8
commit 5039eddc19
3 changed files with 15 additions and 1 deletions
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3
fs/btrfs/transaction.c
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@@ -474,6 +474,7 @@ again:
h->type = type;
h->allocating_chunk = false;
h->reloc_reserved = false;
h->sync = false;
INIT_LIST_HEAD(&h->qgroup_ref_list);
INIT_LIST_HEAD(&h->new_bgs);
@@ -713,7 +714,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
btrfs_create_pending_block_groups(trans, root);
trans->delayed_ref_updates = 0;
if (btrfs_should_throttle_delayed_refs(trans, root)) {
if (!trans->sync && btrfs_should_throttle_delayed_refs(trans, root)) {
cur = max_t(unsigned long, cur, 1);
trans->delayed_ref_updates = 0;
btrfs_run_delayed_refs(trans, root, cur);