On Mon, Apr 11, 2016 at 05:37:40PM -0400, Josef Bacik wrote: > Using the offwakecputime bpf script I noticed most of our time was spent > waiting > on the delayed ref throttling. This is what is supposed to happen, but > sometimes the transaction can commit and then we're waiting for throttling > that > doesn't matter anymore. So change this stuff to be a little smarter by > tracking > the transid we were in when we initiated the throttling. If the transaction > we > get is different then we can just bail out. This resulted in a 50% speedup in > my fs_mark test, and reduced the amount of time spent throttling by 60 seconds > over the entire run (which is about 30 minutes). Thanks, > > Signed-off-by: Josef Bacik <jba...@fb.com> > --- > fs/btrfs/ctree.h | 2 +- > fs/btrfs/extent-tree.c | 15 ++++++++++++--- > fs/btrfs/inode.c | 1 + > fs/btrfs/transaction.c | 3 ++- > 4 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index 55a24c5..4222936 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -3505,7 +3505,7 @@ void btrfs_put_block_group(struct > btrfs_block_group_cache *cache); > int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans, > struct btrfs_root *root, unsigned long count); > int btrfs_async_run_delayed_refs(struct btrfs_root *root, > - unsigned long count, int wait); > + unsigned long count, u64 transid, int wait); > int btrfs_lookup_data_extent(struct btrfs_root *root, u64 start, u64 len); > int btrfs_lookup_extent_info(struct btrfs_trans_handle *trans, > struct btrfs_root *root, u64 bytenr, > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 4b5a517..f23f426 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -2839,6 +2839,7 @@ int btrfs_should_throttle_delayed_refs(struct > btrfs_trans_handle *trans, > > struct async_delayed_refs { > struct btrfs_root *root; > + u64 transid; > int count; > int error; > int sync; > @@ -2854,9 +2855,16 @@ static void delayed_ref_async_start(struct btrfs_work > *work) > > async = container_of(work, struct async_delayed_refs, work); > > - trans = btrfs_join_transaction(async->root); > + trans = btrfs_attach_transaction(async->root); > if (IS_ERR(trans)) { > - async->error = PTR_ERR(trans); > + if (PTR_ERR(trans) != -ENOENT) > + async->error = PTR_ERR(trans); > + goto done; > + }
This ends up deadlocking because btrfs_attach_transaction waits in ways that join does not. The differences between these two are really subtle, and we manage to make this mistake every year or so. Subject: [PATCH] btrfs: fix deadlock in delayed_ref_async_start "Btrfs: track transid for delayed ref flushing" was deadlocking on btrfs_attach_transaction because its not safe to call from the async delayed ref start code. This commit brings back btrfs_join_transaction instead and checks for a blocked commit. Signed-off-by: Josef Bacik <jba...@fb.com> Signed-off-by: Chris Mason <c...@fb.com> --- fs/btrfs/extent-tree.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 6ce5b6c..44da4ac 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -2845,16 +2845,13 @@ static void delayed_ref_async_start(struct btrfs_work *work) async = container_of(work, struct async_delayed_refs, work); - trans = btrfs_attach_transaction(async->root); - if (IS_ERR(trans)) { - if (PTR_ERR(trans) != -ENOENT) - async->error = PTR_ERR(trans); + /* if the commit is already started, we don't need to wait here */ + if (btrfs_transaction_blocked(async->root->fs_info)) goto done; - } - /* Don't bother flushing if we got into a different transaction */ - if (trans->transid != async->transid) { - btrfs_end_transaction(trans, async->root); + trans = btrfs_join_transaction(async->root); + if (IS_ERR(trans)) { + async->error = PTR_ERR(trans); goto done; } @@ -2863,10 +2860,15 @@ static void delayed_ref_async_start(struct btrfs_work *work) * wait on delayed refs */ trans->sync = true; + + /* Don't bother flushing if we got into a different transaction */ + if (trans->transid > async->transid) + goto end; + ret = btrfs_run_delayed_refs(trans, async->root, async->count); if (ret) async->error = ret; - +end: ret = btrfs_end_transaction(trans, async->root); if (ret && !async->error) async->error = ret; -- 2.8.0.rc2 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html