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

David Rientjes
2010-02-11T09:19:50Z

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.