Re: upcoming kerneloops.org item: get_page_from_freelist

[Pekka Enberg]

Hi Andrew,

On Wed, 24 Jun 2009 08:07:53 -0700 Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote:
>> a new item is coming up fast in the kerneloops.org stats, and it's new
>> in 2.6.31-rc;
>>
>> http://www.kerneloops.org/searchweek.php?search=get_page_from_freelist
>>
>> it's this warning in mm/page_alloc.c:
>>
>>                         * __GFP_NOFAIL is not to be used in new code.
>>                          *
>>                          * All __GFP_NOFAIL callers should be fixed so that they
>>                          * properly detect and handle allocation failures.
>>                          *
>>                          * We most definitely don't want callers attempting to
>>                          * allocate greater than single-page units with
>>                          * __GFP_NOFAIL.
>>                          */
>>                         WARN_ON_ONCE(order > 0);
>>
>>
>> typical backtraces look like
>>
>> get_page_from_freelist
>> __alloc_pages_nodemask
>> alloc_pages_current
>> alloc_slab_page
>> new_slab
>> __slab_alloc
>> kmem_cache_alloc_notrace
>> start_this_handle
>> jbd2_journal_start
>>
>> and
>>
>> get_page_from_freelist
>> __alloc_pages_nodemask
>> alloc_pages_current
>> alloc_slab_page
>> new_slab
>> __slab_alloc
>> kmem_cache_alloc_notrace
>> start_this_handle
>> journal_start
>> ext3_journal_start_sb
>> ext3_journal_start
>> ext3_dirty_inode
>>
>> but there are some other ones as well at the url above.
>>
>>
>> git blame shows that
>>
>> commit dab48dab37d2770824420d1e01730a107fade1aa
>> Author: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Date:   Tue Jun 16 15:32:37 2009 -0700
>>
>> introduced this WARN_ON.....

On Wed, Jun 24, 2009 at 7:46 PM, Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> Well yes.  Using GFP_NOFAIL on a higher-order allocation is bad.  This
> patch is there to find, name, shame, blame and hopefully fix callers.
>
> A fix for cxgb3 is in the works.  slub's design is a big problem.
>
> But we'll probably have to revert it for 2.6.31 :(

How is SLUB's design a problem here? Can't we just clear GFP_NOFAIL
from the higher order allocation and thus force GFP_NOFAIL allocations
to use the minimum required order?

                              Pekka
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