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From: Daniel Phillips <phillips@bonn-fries.net>
To: Sven Heinicke <sven@research.nj.nec.com>, linux-kernel@vger.kernel.org
Subject: Re: Google's mm problem - not reproduced on 2.4.13
Date: Fri, 2 Nov 2001 19:11:17 +0100
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Cc: Ben Smith <ben@google.com>, Andrea Arcangeli <andrea@suse.de>,
        Rik van Riel <riel@conectiva.com.br>
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On November 2, 2001 06:51 pm, Sven Heinicke wrote:
> Ben Smith writes:
>  >  > On October 31, 2001 09:45 pm, Andrea Arcangeli wrote:
>  >  >
>  >  >>On Wed, Oct 31, 2001 at 09:39:12PM +0100, Daniel Phillips wrote:
>  >  >>
>  >  >>>On October 31, 2001 07:06 pm, Daniel Phillips wrote:
>  >  >>>
>  >  >>>>I just tried your test program with 2.4.13, 2 Gig, and it ran
>  >  >>>>without problems.  Could you try that over there and see if you
>  >  >>>>get the same result?  If it does run, the next move would be to
>  >  >>>>check with 3.5 Gig.
>  >  >>>>
>  >  >>>Ben reports that his test with 2 Gig memory runs fine, as it does
>  >  >>>for me, but that it locks up tight with 3.5 Gig, requiring power
>  >  >>>cycle.  Since I only have 2 Gig here I can't reproduce that (yet).
>  >  >>>
>  >  >>are you sure it isn't an oom condition. can you reproduce on
>  >  >>2.4.14pre5aa1? mainline (at least before pre6) could deadlock with
>  >  >>too much mlocked memory.
>  >  >>
>  >  >
>  >  > I don't know, I can't reproduce it here, I don't have enough memory.
>  >  > Ben?
>  > 
>  > My test application gets killed (I believe by the oom handler). dmesg
>  > complains about a lot of 0-order allocation failures. For this test,
>  > I'm running with 2.4.14pre5aa1, 3.5gb of RAM, 2 PIII 1Ghz.
>  >   - Ben
>  > 
>  > Ben Smith
>  > Google, Inc
>  > 
> 
> 
> This is a System with 4G of memory and regular swap.  With 2 Pentium
> III 1Ghz processors.
> 
> On 2.4.14-pre6aa1 it happily runs until:
> 
> munmap'ed 7317d000
> Loading data at 7317d000 for slot 2
> Load (/mnt/sdb/sven/chunk10) succeeded!
> mlocking slot 2, 7317d000
> mlocking at 7317d000 of size 1048576
> Connection to hera closed by remote host.
> Connection to hera closed.
> 
> Where is kills my ssh and other programs.  fills my /var/log/messages
> with:
> 
> Nov  2 11:29:07 ps2 kernel: __alloc_pages: 0-order allocation failed (gfp=0x1d2/0)
> Nov  2 11:29:07 ps2 syslogd: select: Cannot allocate memory
> Nov  2 11:29:07 ps2 kernel: __alloc_pages: 0-order allocation failed (gfp=0x1d2/0)
> Nov  2 11:29:07 ps2 kernel: __alloc_pages: 0-order allocation failed (gfp=0x1f0/0)
> Nov  2 11:29:07 ps2 last message repeated 2 times
> 
> a bunch of times.  Then doesn't free the mmaped memory until file
> system is unmounted.

Not freeing the memory is expected and normal.  The previously-mlocked file 
data remains cached in that memory, and even though it's not free, it's 
'easily freeable' so there's no smoking gun there.  The reason the memory is 
freed on umount is, there's no possibility that that file data can be 
referenced again and it makes sense to free it up immediately.

On the other hand, the 0-order failures and oom-kills indicate a genuine bug.

> It never starts going into swap.
> 
> 2.4.14-pre5aa1 does about the same.

--
Daniel
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