Re: [patch 6/7 -mm] oom: avoid oom killer for lowmem allocations

Rik van Riel
2010-02-11T14:09:26Z

On 02/11/2010 04:19 AM, David Rientjes wrote:
> On Wed, 10 Feb 2010, Rik van Riel wrote:
>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -1914,6 +1914,9 @@ rebalance:
>>> * running out of options and have to consider going OOM
>>> */
>>> if (!did_some_progress) {
>>> + /* The oom killer won't necessarily free lowmem */
>>> + if (high_zoneidx< ZONE_NORMAL)
>>> + goto nopage;
>>> if ((gfp_mask& __GFP_FS)&& !(gfp_mask& __GFP_NORETRY)) {
>>> if (oom_killer_disabled)
>>> goto nopage;
>>
>> Are there architectures that only have one memory zone?
>>
>
> It actually ends up not to matter because of how gfp_zone() is implemented
> (and you can do it with mem= on architectures with larger ZONE_DMA zones
> such as ia64). ZONE_NORMAL is always guaranteed to be defined regardless
> of architecture or configuration because it's the default zone for memory
> allocation unless specified by a bit in GFP_ZONEMASK, it doesn't matter
> whether it actually has memory or not. high_zoneidx in this case is just
> gfp_zone(gfp_flags) which always defaults to ZONE_NORMAL when one of the
> GFP_ZONEMASK bits is not set. Thus, the only way to for the conditional
> in this patch to be true is when __GFP_DMA, or __GFP_DMA32 for x86_64, is
> passed to the page allocator and CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is
> enabled, respectively.

Fair enough.

Acked-by: Rik van Riel <riel@redhat.com>

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