Re: Vanilla-Kernel 3 - page allocation failure

[Philipp Herz - Profihost AG]

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


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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