On Wed, 10 Aug 2011 16:14:25 +0200 Michal Hocko <mhocko@xxxxxxx> wrote: > On Tue 09-08-11 19:09:33, KAMEZAWA Hiroyuki wrote: > > memcg :avoid node fallback scan if possible. > > > > Now, try_to_free_pages() scans all zonelist because the page allocator > > should visit all zonelists...but that behavior is harmful for memcg. > > Memcg just scans memory because it hits limit...no memory shortage > > in pased zonelist. > > > > For example, with following unbalanced nodes > > > > Node 0 Node 1 > > File 1G 0 > > Anon 200M 200M > > > > memcg will cause swap-out from Node1 at every vmscan. > > > > Another example, assume 1024 nodes system. > > With 1024 node system, memcg will visit 1024 nodes > > pages per vmscan... This is overkilling. > > > > This is why memcg's victim node selection logic doesn't work > > as expected. > > > > This patch is a help for stopping vmscan when we scanned enough. > > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > OK, I see the point. At first I was afraid that we would make a bigger > pressure on the node which triggered the reclaim but as we are selecting > t dynamically (mem_cgroup_select_victim_node) - round robin at the > moment - it should be fair in the end. More targeted node selection > should be even more efficient. > > I still have a concern about resize_limit code path, though. It uses > memcg direct reclaim to get under the new limit (assuming it is lower > than the current one). > Currently we might reclaim nr_nodes * SWAP_CLUSTER_MAX while > after your change we have it at SWAP_CLUSTER_MAX. This means that > mem_cgroup_resize_mem_limit might fail sooner on large NUMA machines > (currently it is doing 5 rounds of reclaim before it gives up). I do not > consider this to be blocker but maybe we should enhance > mem_cgroup_hierarchical_reclaim with a nr_pages argument to tell it how > much we want to reclaim (min(SWAP_CLUSTER_MAX, nr_pages)). > What do you think? > Hmm, > mem_cgroup_resize_mem_limit might fail sooner on large NUMA machines mem_cgroup_resize_limit() just checks (curusage < prevusage), then, I agree reducing the number of scan/reclaim will cause that. I agree to pass nr_pages to try_to_free_mem_cgroup_pages(). Thanks, -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>