Messages in this thread | | | Date | Fri, 24 Feb 2006 00:47:26 -0500 | From | John McCutchan <> | Subject | Re: udevd is killing file write performance. |
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On Thu, Feb 23, 2006 at 04:14:25PM -0800, Andrew Morton wrote: > John McCutchan <john@johnmccutchan.com> wrote: > > > > ... > > > > > > I have a bad feeling about this one. It'd be nice to have an exact > > > understanding of the problen source, but if it's just lots of traffic on > > > ->d_lock we're kinda stuck. I don't expect we'll run off and RCUify > > > d_parent or turn d_lock into a seq_lock or anything liek that. > > > > > > Then again, maybe making d_lock an rwlock _will_ help - if this workload is > > > also hitting tree_lock (Robin?) and we're not seeing suckiness due to that > > > then perhaps the rwlock is magically helping. > > > > > > > > > > instead of your hack. > > > > > > It's not a terribly bad hack - it's just poor-man's hashing, and it's > > > reasonably well-suited to the sorts of machines and workloads which we > > > expect will hit this problem. > > > > > > > If this is as good as it gets, here is a patch (totally untested). > > > > ... > > @@ -538,7 +537,7 @@ > > struct dentry *parent; > > struct inode *inode; > > > > - if (!atomic_read (&inotify_watches)) > > + if (!atomic_read (&dentry->d_sb->s_inotify_watches)) > > return; > > > > What happens here if we're watching a mountpoint - the parent is on a > different fs?
There are four cases to consider here.
Case 1: parent fs watched and child fs watched correct results Case 2: parent fs watched and child fs not watched We may not deliver an event that should be delivered. Case 3: parent fs not watched and child fs watched We take d_lock when we don't need to Case 4: parent fs not watched and child fs not watched correct results
Case 2 screws us. We have to take the lock to even look at the parent's dentry->d_sb->s_inotify_watches. I don't know of a way around this one.
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