linux-kernel - Re: bad rss-counter message in 3.14rc5

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Date:	Tue, 18 Mar 2014 19:12:14 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Sasha Levin <sasha.levin@...cle.com>
cc:	Hugh Dickins <hughd@...gle.com>, Dave Jones <davej@...hat.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Bob Liu <bob.liu@...cle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>
Subject: Re: bad rss-counter message in 3.14rc5

On Tue, 18 Mar 2014, Sasha Levin wrote:
> On 03/18/2014 08:38 PM, Hugh Dickins wrote:
> > On Tue, 11 Mar 2014, Dave Jones wrote:
> > > On Tue, Mar 11, 2014 at 09:36:03PM +0400, Cyrill Gorcunov wrote:
> > >   > On Tue, Mar 11, 2014 at 01:10:45PM -0400, Dave Jones wrote:
> > >   > >  >
> > >   > >  > Dave, iirc trinity can write log file pointing which exactly
> > > syscall sequence
> > >   > >  > was passed, right? Share it too please.
> > >   > >
> > >   > > Hm, I may have been mistaken, and the damage was done by a previous
> > > run.
> > >   > > I went from being able to reproduce it almost instantly to now not
> > > being able
> > >   > > to reproduce it at all.  Will keep trying.
> > >   >
> > >   > Sasha already gave a link to the syscalls sequence, so no rush.
> > > 
> > > It'd be nice to get a more concise reproducer, his list had a little of
> > > everything in there.
> > 
> > I've so far failed to find any explanation for your swapops.h BUG;
> > but believe I have identified one cause for "Bad rss-counter"s.
> > 
> > My hunch is that the swapops.h BUG is "nearby", but I just cannot
> > fit it together (the swapops.h BUG comes when rmap cannot find all
> > all the migration entries it inserted earlier: it's a very useful
> > BUG for validating rmap).
> > 
> > Untested patch below: I can't quite say Reported-by, because it may
> > not even be one that you and Sasha have been seeing; but I'm hopeful,
> > remap_file_pages is in the list.
> > 
> > Please give this a try, preferably on 3.14-rc or earlier: I've never
> > seen "Bad rss-counter"s there myself (trinity uses remap_file_pages
> > a lot more than most of us); but have seen them on mmotm/next, so
> > some other trigger is coming up there, I'll worry about that once
> > it reaches 3.15-rc.
> 
> The patch fixed the "Bad rss-counter" errors I've been seeing both in
> 3.14-rc7 and -next.

Great, thanks a lot, Sasha.  I was afraid that you'd hit those swapops
BUGs, which seemed perhaps to be paired with these; but glad to hear
a positive.  Let's see how Dave fares.  (I've not forgotten shmem
fallocate, by the way, but those probably aren't as high on my agenda
as you'd like.)

Hugh
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