Re: Vanilla-Kernel 3 - page allocation failure

[Philipp Herz - Profihost AG <p.herz@profihost.ag>]

Am 26.10.2011 22:26, schrieb David Rientjes:
> On Mon, 24 Oct 2011, Philipp Herz - Profihost AG wrote:
>
>> we have recompiled the kernel of one machine with CONFIG_SLUB instead of
>> CONFIG_SLAB, but it is showing similar message.
>>
>> Now it's showing failure at "order:5, mode:0x4020".
>>
>> Call trace can be found at:
>> * http://pastebin.com/uGJiwvG1
>>
>> Comparing kernel 2.6.32 (mm/page_alloc.c) there seams to be the same way of
>> dealing with page allocation.
>>
>> Do you have an idea why these (warning) messages do never appear running
>> 2.6.32?
>>
>
> Do you have CONFIG_COMPACTION enabled?  Perhaps this is a difference in
> the deprecation of lumpy reclaim between 2.6.35 and 2.6.38 and
> defragmentation being done by memory compaction instead.
Yes CONFIG_COMPACTION is enabled as a dependency for 
TRANSPARENT_HUGEPAGE which is different to the configs before.

>
> It won't be triggered synchronously in this context since it's a
> GFP_ATOMIC allocation, which is why it emits a page allocation failure in
> the first place, but it will show whether defragmentation is the issue or
> you're just simply low on memory.
Do you mean that "memory compaction" should be turned off again?

How can I see the difference between "deframentation issue" and "low 
memory"? I did not get this point.