On Mon, Sep 09, 2013 at 04:46:55PM -0400, J. Bruce Fields wrote:
> On Mon, Sep 09, 2013 at 01:46:47AM +0100, Al Viro wrote:
> > On Sat, Sep 07, 2013 at 02:46:01PM -0400, J. Bruce Fields wrote:
> > > From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
> > >
> > > DCACHE_DISCONNECTED should not be cleared until we're sure the dentry is
> > > connected all the way up to the root of the filesystem. It *shouldn't*
> > > be cleared as soon as the dentry is connected to a parent. That will
> > > cause bugs at least on exportable filesystems.
> >
> > Then you probably want this
> > if (!IS_ROOT(pd)) {
> > /* must have found a connected parent - great */
> > spin_lock(&pd->d_lock);
> > pd->d_flags &= ~DCACHE_DISCONNECTED;
> > spin_unlock(&pd->d_lock);
> > noprogress = 0;
> > to go through all intermediates, clearing DCACHE_DISCONNECTED on all of
> > them; O(depth^2) can suck when we have a long chain of directories...
>
> I'm not sure what you mean--something like the following?
>
> Not having seen complaints about filehandle lookup performance I'm
> inclined to leave it alone, though.
But just for fun--I did some cleanup and fixed some other quadratic
behavior here and can notice a difference on lookups of very deep
subdirectories.
For example I'm seeing an uncached lookup of an 8000-deep directory
taking about 6 seconds, and can get that down to a tenth of a second.
I'm not sure yet if the difference on less extreme examples is really
significant, I need to experiment some more.
I'll do some more review and post patches and results.
--b.
> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> index 5816e19..72ed705 100644
> --- a/fs/exportfs/expfs.c
> +++ b/fs/exportfs/expfs.c
> @@ -90,6 +90,22 @@ find_disconnected_root(struct dentry *dentry)
> return dentry;
> }
>
> +static void clear_disconnected(struct dentry *dentry)
> +{
> + dget(dentry);
> + while (dentry->d_flags & DCACHE_DISCONNECTED) {
> + struct dentry *parent = dget_parent(dentry);
> +
> + spin_lock(&dentry->d_lock);
> + dentry->d_flags &= ~DCACHE_DISCONNECTED;
> + spin_unlock(&dentry->d_lock);
> +
> + dput(dentry);
> + dentry = parent;
> + }
> + dput(dentry);
> +}
> +
> /*
> * Make sure target_dir is fully connected to the dentry tree.
> *
> @@ -114,15 +130,11 @@ reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
>
> if (!IS_ROOT(pd)) {
> /* must have found a connected parent - great */
> - spin_lock(&pd->d_lock);
> - pd->d_flags &= ~DCACHE_DISCONNECTED;
> - spin_unlock(&pd->d_lock);
> + clear_disconnected(target_dir);
> noprogress = 0;
> } else if (pd == mnt->mnt_sb->s_root) {
> printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
> - spin_lock(&pd->d_lock);
> - pd->d_flags &= ~DCACHE_DISCONNECTED;
> - spin_unlock(&pd->d_lock);
> + clear_disconnected(target_dir);
> noprogress = 0;
> } else {
> /*
--
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