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

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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@xxxxxxxxxx>

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