linux-kernel - Re: Vanilla-Kernel 3 - page allocation failure

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Date:	Tue, 18 Oct 2011 15:24:44 +0200
From:	Philipp Herz - Profihost AG <p.herz@...fihost.ag>
To:	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Vanilla-Kernel 3 - page allocation failure

Hello Cascardo

 > Usually, after the stack dump, there is some
 > statistics about memory.
Yes, i have seen this in other posts as well.

 > I have seen that these may be suppressed
 > if you have a NUMA system with lots of nodes.
Yes, in our case it seems to be suppressed.

 > Check for NODE_SHIFT in your
 > config. If it's greater than 8, that output may have been suppressed.
CONFIG_NODES_SHIFT=10 will be the answer.

Is there any way to get those stats without recompiling the kernel?

 > But you may have just ignored the statistics because of the
 > stack dump.
No, i was also wondering why other do have these ;-)

Regards,
Philipp

Am 18.10.2011 14:38, schrieb Thadeu Lima de Souza Cascardo:
> On Tue, Oct 18, 2011 at 02:07:38PM +0200, Philipp Herz - Profihost AG wrote:
>> Hello Cascardo,
>>
>> thanks for your detailed answer!
>>
>> I have uploaded two call traces to pastebin for further investigation.
>>
>> Maybe this can help you.
>>
>> * http://pastebin.com/Psg2dGYC (kworker)
>> * http://pastebin.com/pPFjZqxL (php5)
>>
>> Regards,
>> Philipp
>>
>
> Hello, Philipp.
>
> That only tells us that you have a TCP workload in your system. This is
> the subsystem that is trying to allocate memory. However, we do not know
> why there is failure. Usually, after the stack dump, there is some
> statistics about memory. I have seen that these may be suppressed if you
> have a NUMA system with lots of nodes. Check for NODE_SHIFT in your
> config. If it's greater than 8, that output may have been suppressed.
> But you may have just ignored the statistics because of the stack dump.
>
> Regards,
> Cascardo.
>
>>
>> Am 18.10.2011 13:32, schrieb Thadeu Lima de Souza Cascardo:
>>> On Tue, Oct 18, 2011 at 12:25:03PM +0200, Philipp Herz - Profihost AG wrote:
>>>> After updating kernel (x86_64) to stable version 3 there are a few
>>>> messages appearing in the kernel log such as
>>>>
>>>> kworker/0:1: page allocation failure: order:1, mode:0x20
>>>> mysql: page allocation failure: order:1, mode:0x20
>>>> php5: page allocation failure: order:1, mode:0x20
>>>>
>>>> Searching the net showed that these messages are known to occur since 2004.
>>>>
>>>> Some people were able to get rid of them by setting
>>>> /proc/sys/vm/min_free_kbytes to a high enough value. This does not
>>>> help in our case.
>>>>
>>>>
>>>> Is there a kernel comand line argument to avoid these messages?
>>>>
>>>> As of mm/page_alloc.c these messages are marked to be only warning
>>>> messages and would not appear if 'gpf_mask' was set to __GFP_NOWARN
>>>> in function warn_alloc_failed.
>>>>
>>>> How does this mask get set? Is it set by the "external" process
>>>> knocking at the memory manager?
>>>>
>>>
>>> Hello, Philipp.
>>>
>>> This happens when kernel tries to allocate memory, sometimes in response
>>> to some request by the user space, but also in other contexts. For
>>> example, an interrupt by a network driver may try to allocate memory. In
>>> this context, it will use GFP_ATOMIC as a mask, for example. The most
>>> usual flags in the kernel are GFP_KERNEL and GFP_ATOMIC.
>>>
>>>> What is the magic behind the 'order' and 'mode'?
>>>>
>>>
>>> The order is the binary log of the number of pages requested. So, order 1
>>> allocations are 2 pages, order 4 would be 16 pages, for example.
>>>
>>> The mode is, in fact, gfp_flags. 0x20 is GFP_ATOMIC. This kind of
>>> allocation cannot do IO or access the filesystem. Also, it cannot wait
>>> for reclaim memory from cache.
>>>
>>> This warning is usually followed by some statistics about memory use
>>> in your system. Please post it to give more information about this
>>> situation.
>>>
>>> I have watched some of this happen when lots of cache is used by some
>>> filesystems. Perhaps, some tweaking of the vm sysctl options may help,
>>> but I can point any magic tweaking right now.
>>>
>>> Regards,
>>> Cascardo.
>>>
>>>> I'm not a subscriber, so please CC me a copy of messages related to
>>>> the subject. I'm not sure if I can help much by looking at the
>>>> inside of the kernel, but I will try my best to answer any questions
>>>> concerning this issue.
>>>>
>>>> Best regards, Philipp
>>>> --
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>>>
>>
>
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