Messages in this thread | | | From | Miklos Szeredi <> | Date | Wed, 19 Jul 2017 22:24:05 +0200 | Subject | Re: [PATCH 1/4] fs/dcache: Limit numbers of negative dentries |
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On Mon, Jul 17, 2017 at 3:39 PM, Waiman Long <longman@redhat.com> wrote: > The number of positive dentries is limited by the number of files > in the filesystems. The number of negative dentries, however, > has no limit other than the total amount of memory available in > the system. So a rogue application that generates a lot of negative > dentries can potentially exhaust most of the memory available in the > system impacting performance on other running applications. > > To prevent this from happening, the dcache code is now updated to limit > the amount of the negative dentries in the LRU lists that can be kept > as a percentage of total available system memory. The default is 5% > and can be changed by specifying the "neg_dentry_pc=" kernel command > line option. > > Signed-off-by: Waiman Long <longman@redhat.com> > ---
[...]
> @@ -603,7 +698,13 @@ static struct dentry *dentry_kill(struct dentry *dentry) > > if (!IS_ROOT(dentry)) { > parent = dentry->d_parent; > - if (unlikely(!spin_trylock(&parent->d_lock))) { > + /* > + * Force the killing of this negative dentry when > + * DCACHE_KILL_NEGATIVE flag is set. > + */ > + if (unlikely(dentry->d_flags & DCACHE_KILL_NEGATIVE)) { > + spin_lock(&parent->d_lock);
This looks like d_lock ordering problem (should be parent first, child second). Why is this needed, anyway?
> + } else if (unlikely(!spin_trylock(&parent->d_lock))) { > if (inode) > spin_unlock(&inode->i_lock); > goto failed;
Thanks, Miklos
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