linux-kernel - Re: linux-next: slab shrinkers: BUG at mm/list

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Message-ID: <20130626082220.GG28748@dhcp22.suse.cz>
Date:	Wed, 26 Jun 2013 10:22:20 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Glauber Costa <glommer@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: slab shrinkers: BUG at mm/list_lru.c:92

On Sun 23-06-13 15:51:29, Glauber Costa wrote:
> On Fri, Jun 21, 2013 at 11:00:21AM +0200, Michal Hocko wrote:
> > On Thu 20-06-13 17:12:01, Michal Hocko wrote:
> > > I am bisecting it again. It is quite tedious, though, because good case
> > > is hard to be sure about.
> > 
> > OK, so now I converged to 2d4fc052 (inode: convert inode lru list to generic lru
> > list code.) in my tree and I have double checked it matches what is in
> > the linux-next. This doesn't help much to pin point the issue I am
> > afraid :/
> > 
> Can you revert this patch (easiest way ATM is to rewind your tree to a point
> right before it) and apply the following patch?

OK, I am testing it now.

> As Dave has mentioned, it is very likely that this bug was already there, we
> were just not ever checking imbalances. The attached patch would tell us at
> least if the imbalance was there before.

Maybe I wasn't clear before but I have seen mostly hangs (posted
earlier) during bisection. I do not remember BUG_ONs on imbalances after
inode_lru_isolate fix.

> If this is the case, I would suggest
> turning the BUG condition into a WARN_ON_ONCE since we would be officially
> not introducing any regression. It is no less of a bug, though, and we should
> keep looking for it.
> 
> The main change from before / after the patch is that we are now keeping things
> per node. One possibility of having this BUGing would be to have an inode to be
> inserted into one node-lru and removed from another. I cannot see how it could
> happen, because kernel pages are stable in memory and are not moved from node
> to node. We could still have some sort of weird bug in the node calculation
> function. 

> In any case, would it be possible for you to artificially restrict
> your setup to a single node ? Although I have no idea how to do that, we seem
> to have no parameter to disable numa. Maybe booting with less memory, enough to
> fit a single node?

I can play with memmap to use areas on from a single node. Let's see
whether the patch in the follow up email shows something first.
-- 
Michal Hocko
SUSE Labs
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