Re: [PATCH 1/2] mm: vmscan: Limit direct reclaim for higher order allocations

[Minchan Kim <minchan.kim@gmail.com>]

On Fri, Oct 07, 2011 at 04:17:22PM +0100, Mel Gorman wrote:
> From: Rik van Riel <riel@redhat.com>
> 
> When suffering from memory fragmentation due to unfreeable pages,
> THP page faults will repeatedly try to compact memory.  Due to the
> unfreeable pages, compaction fails.
> 
> Needless to say, at that point page reclaim also fails to create
> free contiguous 2MB areas.  However, that doesn't stop the current
> code from trying, over and over again, and freeing a minimum of 4MB
> (2UL << sc->order pages) at every single invocation.
> 
> This resulted in my 12GB system having 2-3GB free memory, a
> corresponding amount of used swap and very sluggish response times.
> 
> This can be avoided by having the direct reclaim code not reclaim from
> zones that already have plenty of free memory available for compaction.
> 
> If compaction still fails due to unmovable memory, doing additional
> reclaim will only hurt the system, not help.
> 
> Signed-off-by: Rik van Riel <riel@redhat.com>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

-- 
Kinds regards,
Minchan Kim