Re: [PATCH 8/8] inode: don't softlockup when evicting inodes

[Josef Bacik]

On 04/01/2015 04:05 AM, Jan Kara wrote:
>    Sorry for a late reply. I was ill last week...

That's ok, I was on vacation for the last two weeks ;).

> On Fri 20-03-15 13:14:16, Josef Bacik wrote:
> > On a box with a lot of ram (148gb) I can make the box softlockup after running
> > an fs_mark job that creates hundreds of millions of empty files.  This is
> > because we never generate enough memory pressure to keep the number of inodes on
> > our unused list low, so when we go to unmount we have to evict ~100 million
> > inodes.  This makes one processor a very unhappy person, so add a cond_resched()
> > in dispose_list() and cond_resched_lock() in the eviction isolation function to
> > combat this.  Thanks,
> >
> > Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> > ---
> >   fs/inode.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index b961e5a..c58dbd3 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -574,6 +574,7 @@ static void dispose_list(struct list_head *head)
> >   		list_del_init(&inode->i_lru);
> >
> >   		evict(inode);
> > +		cond_resched();
>    Fine.
>
> >   	}
> >   }
> >
> > @@ -592,6 +593,7 @@ void evict_inodes(struct super_block *sb)
> >   	LIST_HEAD(dispose);
> >
> >   	spin_lock(&sb->s_inode_list_lock);
> > +again:
> >   	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
> >   		if (atomic_read(&inode->i_count))
> >   			continue;
> > @@ -606,6 +608,14 @@ void evict_inodes(struct super_block *sb)
> >   		inode_lru_list_del(inode);
> >   		spin_unlock(&inode->i_lock);
> >   		list_add(&inode->i_lru, &dispose);
> > +
> > +		/*
> > +		 * We can have a ton of inodes to evict at unmount time given
> > +		 * enough memory, check to see if we need to go to sleep for a
> > +		 * bit so we don't livelock.
> > +		 */
> > +		if (cond_resched_lock(&sb->s_inode_list_lock))
> > +			goto again;
>    Not so fine. How this is ever guaranteed to finish? We don't move inodes
> from the i_sb_list in this loop so if we ever take 'goto again' we just
> start doing all the work from the beginning...
>
> What needs to happen is that if we need to resched, we drop
> sb->s_inode_list_lock, call dispose_list(&dispose) and *then* restart from
> the beginning since we have freed all the inodes that we isolated...

Ooops, good point.  I'll get this fixed up, thanks,

Josef
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