| Message ID | 20130909204655.GA10599@fieldses.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@redhat.com> > > > > > > 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 { > /* -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Oct 11, 2013 at 12:02:37PM -0400, J. Bruce Fields wrote: > 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. This sounds like and awesome improvement. How much code do you have to add for it? -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sat, Oct 12, 2013 at 01:42:35AM -0700, Christoph Hellwig wrote: > On Fri, Oct 11, 2013 at 12:02:37PM -0400, J. Bruce Fields wrote: > > 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. > > This sounds like and awesome improvement. Nobody should be nesting that deep, but maybe it's useful to have the insurance against bad behavior anyway. > How much code do you have to > add for it? fs/exportfs/expfs.c | 224 ++++++++++++++++++++++++++-------------------------- 1 file changed, 112 insertions(+), 112 deletions(-) But maybe I removed some necessary complication. I'll post the patches.... --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 { /*