Re: upcoming kerneloops.org item: get_page_from_freelist

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Wed, Jun 24, 2009 at 7:55 PM, Pekka Enberg<penberg@cs.helsinki.fi> wrote:
> Hi Andrew,
>
> On Wed, 24 Jun 2009 08:07:53 -0700 Arjan van de Ven <arjan@infradead.org> 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@linux-foundation.org>
>>> 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@linux-foundation.org> 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?

Small correction: force GFP_NOFAIL allocations to use minimum order
_if_ the higher order allocation fails.