On Wed, Jul 25, 2012 at 10:35:08PM +0100, Mel Gorman wrote: > On Wed, Jul 25, 2012 at 12:59:48PM -0700, Greg KH wrote: > > On Mon, Jul 23, 2012 at 02:38:43PM +0100, Mel Gorman wrote: > > > commit ad2b8e601099a23dffffb53f91c18d874fe98854 upstream - WARNING: this is a substitute patch. > > > > > > Stable note: Not tracked in Bugzilla. This is a substitute for an > > > upstream commit addressing a completely different issue that > > > accidentally contained an important fix. The workload this patch > > > helps was memcached when IO is started in the background. memcached > > > should stay resident but without this patch it gets swapped more > > > than it should. Sometimes this manifests as a drop in throughput > > > but mostly it was observed through /proc/vmstat. > > > > > > Commit [246e87a9: memcg: fix get_scan_count() for small targets] was > > > meant to fix a problem whereby small scan targets on memcg were ignored > > > causing priority to raise too sharply. It forced scanning to take place > > > if the target was small, memcg or kswapd. > > > > > > >From the time it was introduced it cause excessive reclaim by kswapd > > > with workloads being pushed to swap that previously would have stayed > > > resident. This was accidentally fixed by commit [ad2b8e60: mm: memcg: > > > remove optimization of keeping the root_mem_cgroup LRU lists empty] but > > > that patchset is not suitable for backporting. > > > > > > The original patch came with no information on what workloads it benefits > > > but the cost of it is obvious in that it forces scanning to take place > > > on lists that would otherwise have been ignored such as small anonymous > > > inactive lists. This patch partially reverts 246e87a9 so that small lists > > > are not force scanned which means that IO-intensive workloads with small > > > amounts of anonymous memory will not be swapped. > > > > > > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > > > --- > > > mm/vmscan.c | 3 --- > > > 1 file changed, 3 deletions(-) > > > > I don't understand this patch. The original > > ad2b8e601099a23dffffb53f91c18d874fe98854 commit touched the file > > mm/memcontrol.c and seemed to do something quite different from what you > > have done below. > > > > The main problem is I'm an idiot and "missed" when copying&paste and followed > through with the mistake. The actual commit of interest was the one after it > [b95a2f2d: mm: vmscan: convert global reclaim to per-memcg LRU lists] > > That patch has this hunk in it > > @@ -1886,7 +1886,7 @@ static void get_scan_count(struct mem_cgroup_zone *mz, struct scan_control *sc, > * latencies, so it's better to scan a minimum amount there as > * well. > */ > - if (current_is_kswapd()) > + if (current_is_kswapd() && mz->zone->all_unreclaimable) > force_scan = true; > if (!global_reclaim(sc)) > force_scan = true; > > This change makes it very difficult for kswapd to force scan which was > the fix I was interested in but the series is not suitable for backport. > This has changed again since in 3.5-rc1 due to commit [90126375: mm/vmscan: > push lruvec pointer into get_scan_count()] where this check became > > if (current_is_kswapd() && zone->all_unreclaimable) > > Superficially that looks ok to backport, but it's not due to a subtle > difference in how zone is looked up in the new context. > > Can you use this patch as a replacement? It is functionally much closer > to what happens upstream while still backporting the actual fix of > interest. Yes, that makes more sense as that is what the patch you included does :) I'll go queue it up now, thanks for the backport. greg k-h -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>