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

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Date:	Tue, 18 Mar 2014 22:42:11 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	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 03/18/2014 10:12 PM, Hugh Dickins wrote:
> 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.)

I do hit the swapops issue a lot, I didn't think that your patch was
supposed to fix that so I didn't mention it.

Thanks for keeping shmem in mind, I've removed shmem from testing for now
but I agree, it's not one of the more important issues to be taken care of.


Thanks,
Sasha

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