Re: [PATCH 55 of 66] select CONFIG_COMPACTION if TRANSPARENT_HUGEPAGE enabled

Andrea Arcangeli
2010-12-09T19:06:00Z

On Thu, Nov 18, 2010 at 04:22:45PM +0000, Mel Gorman wrote:
> Just to confirm - by hang, you mean grinds to a slow pace as opposed to
> coming to a complete stop and having to restart?

Hmm it's like if you're gigabytes in swap and apps hangs for a while
and system is not really usable and it swaps for most new memory
allocations despite there's plenty of memory free, but it's not a
deadlock of course.

BTW, alternatively I could:

unsigned long transparent_hugepage_flags __read_mostly =
(1<<TRANSPARENT_HUGEPAGE_FLAG)|
+#ifdef CONFIG_COMPACTION
+ (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
+#endif
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);

That would adds GFP_ATOMIC to THP allocation if compaction wasn't
selected, but I think having compaction enabled diminish the risk of
misconfigured kernels leading to unexpected measurements and behavior,
so I feel much safer to keep the select COMPACTION in this patch.

> Acked-by: Mel Gorman <mel@csn.ul.ie>

Added.

Thanks,
Andrea