> On Fri, Oct 22, 2010 at 11:32:37AM -0500, Christoph Lameter wrote: > > On Fri, 22 Oct 2010, Christoph Hellwig wrote: > > > > > > I think making shrinking decision per-zone is fine. But do we need to > > > duplicate all the lru lists and infrastructure per-zone for that instead > > > of simply per-zone? Even with per-node lists we can easily skip over > > > items from the wrong zone. > > > > > > Given that we have up to 6 zones per node currently, and we would mostly > > > use one with a few fallbacks that seems like a lot of overkill. > > > > Zones can also cause asymmetry in reclaim if per zone reclaim is done. > > > > Look at the following zone setup of a Dell R910: > > > > grep "^Node" /proc/zoneinfo > > Node 0, zone DMA > > Node 0, zone DMA32 > > Node 0, zone Normal > > Node 1, zone Normal > > Node 2, zone Normal > > Node 3, zone Normal > > > > A reclaim that does per zone reclaim (but in reality reclaims all objects > > in a node (or worse as most shrinkers do today in the whole system) will > > put 3x the pressure on node 0. > > No it doesn't. This is how it works: > > node0zoneD has 1% of pagecache for node 0 > node0zoneD32 has 9% of pagecache > node0zoneN has 90% of pagecache > > If there is a memory shortage in all node0 zones, the first zone will > get 1% of the pagecache scanning pressure, dma32 will get 9% and normal > will get 90%, for equal pressure on each zone. > > In my patch, those numbers will pass through to shrinker for each zone, > and ask the shrinker to scan and equal proportion of objects in each of > its zones. > > If you have a per node shrinker, you will get asymmetries in pressures > whenever there is not an equal amount of reclaimable objects in all > the zones of a node. Interesting. your explanation itself seems correct. but it inspire me that there is another issue in both Christoph and your patch. On ideal 32bit highmem system, memory usage are DMA: unused NORMAL: 100% slab, 0% page cache HIGHMEM: 0% slab, 100% page cache So, per-zone slab/page-cache shrinker balancing logic don't works on 32bit x86. kswapd should reclaim some objects from normal zone even if it couldn't reclaim any page cache from normal zone. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>