linux-kernel - Re: [Linux-cachefs] 3.0.3 64-bit Crash running fscache/cachefilesd

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Date:	Thu, 13 Oct 2011 13:48:44 -0700
From:	Mark Moseley <moseleymark@...il.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Linux filesystem caching discussion list 
	<linux-cachefs@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [Linux-cachefs] 3.0.3 64-bit Crash running fscache/cachefilesd

On Thu, Oct 13, 2011 at 8:21 AM, David Howells <dhowells@...hat.com> wrote:
> Mark Moseley <moseleymark@...il.com> wrote:
>
>> So on a cleared cache with SLAB, it took a while but this finally came
>> up. One interesting thing is that at some point, it logged this:
>>
>> [13461.605871] [httpd ] <== __fscache_read_or_alloc_pages() = -ENOBUFS
>> [invalidating]
>
> That's okay.  Basically, a read-from-cache operation was rejected because the
> cache object was in the early phase of being invalidated.  I kept it simple
> here - the read might complete next time it is tried, but it's just a cache so
> that shouldn't matter.

Ok, noted


>> It was a while from when it logged that until when I happened to check
>> on the box again, but when I did (shortly before this traceback),
>> despite constant NFS activity, nothing in the fscache cache was
>> getting written out (i.e. the used bytes on the partition stopped
>> changing), and without any messages about withdrawing the cache or
>> anythin.
>
> Did you look at /proc/fs/fscache/stats at all?

I didn't but I can repeat it. Which of the stats in
/proc/fs/fscache/stats would be best to track?


>> [20839.802118] kernel BUG at fs/fscache/object-list.c:83!
>> [20839.802733] invalid opcode: 0000 [#1] SMP
>
> That fits with the previous BUG elsewhere in object-list.c.  It sounds like
> there's a refcounting problem somewhere.

Any sys or proc settings I should turn on to track that?
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