From 5039eddc19aee8c894191c24f2dde4e645ca1bbb Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 15 Jan 2014 13:34:13 -0500 Subject: [PATCH] Btrfs: make fsync latency less sucky 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 Signed-off-by: Chris Mason --- fs/btrfs/file.c | 12 ++++++++++++ fs/btrfs/transaction.c | 3 ++- fs/btrfs/transaction.h | 1 + 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 030012e1710c..72df63b0c799 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1928,12 +1928,24 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync) if (file->private_data) btrfs_ioctl_trans_end(file); + /* + * We use start here because we will need to wait on the IO to complete + * in btrfs_sync_log, which could require joining a transaction (for + * example checking cross references in the nocow path). If we use join + * here we could get into a situation where we're waiting on IO to + * happen that is blocked on a transaction trying to commit. With start + * we inc the extwriter counter, so we wait for all extwriters to exit + * before we start blocking join'ers. This comment is to keep somebody + * from thinking they are super smart and changing this to + * btrfs_join_transaction *cough*Josef*cough*. + */ trans = btrfs_start_transaction(root, 0); if (IS_ERR(trans)) { ret = PTR_ERR(trans); mutex_unlock(&inode->i_mutex); goto out; } + trans->sync = true; ret = btrfs_log_dentry_safe(trans, root, dentry); if (ret < 0) { diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index da2ac4c6d78b..b16352ce0f73 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -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); diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h index d05b6013fea8..6ac037e9f9f0 100644 --- a/fs/btrfs/transaction.h +++ b/fs/btrfs/transaction.h @@ -93,6 +93,7 @@ struct btrfs_trans_handle { short adding_csums; bool allocating_chunk; bool reloc_reserved; + bool sync; unsigned int type; /* * this root is only needed to validate that the root passed to -- 2.30.2