On Thu, 1 Sep 2011 08:15:40 +0200 Johannes Weiner <jweiner@xxxxxxxxxx> wrote: > On Thu, Sep 01, 2011 at 09:09:31AM +0900, KAMEZAWA Hiroyuki wrote: > > On Wed, 31 Aug 2011 19:13:34 +0900 > > Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > > > > On Wed, Aug 31, 2011 at 6:08 PM, Johannes Weiner <jweiner@xxxxxxxxxx> wrote: > > > > Reclaim decides to skip scanning an active list when the corresponding > > > > inactive list is above a certain size in comparison to leave the > > > > assumed working set alone while there are still enough reclaim > > > > candidates around. > > > > > > > > The memcg implementation of comparing those lists instead reports > > > > whether the whole memcg is low on the requested type of inactive > > > > pages, considering all nodes and zones. > > > > > > > > This can lead to an oversized active list not being scanned because of > > > > the state of the other lists in the memcg, as well as an active list > > > > being scanned while its corresponding inactive list has enough pages. > > > > > > > > Not only is this wrong, it's also a scalability hazard, because the > > > > global memory state over all nodes and zones has to be gathered for > > > > each memcg and zone scanned. > > > > > > > > Make these calculations purely based on the size of the two LRU lists > > > > that are actually affected by the outcome of the decision. > > > > > > > > Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx> > > > > Cc: Rik van Riel <riel@xxxxxxxxxx> > > > > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > > > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > > > Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> > > > > Cc: Balbir Singh <bsingharora@xxxxxxxxx> > > > > > > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > > > > > > I can't understand why memcg is designed for considering all nodes and zones. > > > Is it a mistake or on purpose? > > > > It's purpose. memcg just takes care of the amount of pages. > > This mechanism isn't about memcg at all, it's an aging decision at a > much lower level. Can you tell me how the old implementation is > supposed to work? > Old implemenation was supporsed to make vmscan to see only memcg and ignore zones. memcg doesn't take care of any zones. Then, it uses global numbers rather than zones. Assume a system with 2 nodes and the whole memcg's inactive/active ratio is unbalaned. Node 0 1 Active 800M 30M Inactive 100M 200M If we judge 'unbalance' based on zones, Node1's Active will not rotate even if it's not accessed for a while. If we judge unbalance based on total stat, Both of Node0 and Node 1 will be rotated. Hmm, old one doesn't work as I expexted ? But okay, as time goes, I think Node1's inactive will decreased and then, rotate will happen even with zone based ones. > > But, hmm, this change may be good for softlimit and your work. > > Yes, I noticed those paths showing up in a profile with my patches. > Lots of memcgs on a multi-node machine will trigger it too. But it's > secondary, my primary reasoning was: this does not make sense at all. > your word sounds always too strong to me ;) please be soft. > > I'll ack when you add performance numbers in changelog. > > It's not exactly a performance optimization but I'll happily run some > workloads. Do you have suggestions what to test for? I.e. where > would you expect regressions? > Some comparison about amount of swap-out before/after change will be good. Hm. If I do... - set up x86-64 NUMA box. (fake numa is ok.) - create memcg with 500M limit. - running kernel make with make -j 6(or more) see time of make and amount of swap-out. 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>