Re: [PATCH 55 of 66] select CONFIG_COMPACTION ifTRANSPARENT_HUGEPAGE enabled

[Andrea Arcangeli]

Hi Mel,

On Tue, Dec 14, 2010 at 09:45:56AM +0000, Mel Gorman wrote:
> On Thu, Dec 09, 2010 at 08:04:07PM +0100, Andrea Arcangeli wrote:
> > 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.
> > 
> 
> Ok, but it's likely to be kswapd being very aggressive because it's
> woken up frequently and tries to balance all zones. Once it's not
> deadlocking entirely, there isn't a more fundamental bug hiding in there
> somewhere.

kswapd isn't activated by transhuge allocations because there's
khugepaged for that and it's throttle to try a 2m alloc only once per
minute if there's fragmentation.

So the reason of the trashing is the direct lumpy.
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