On Thu, 21 Apr 2011 22:53:19 -0700 Ying Han <yinghan@xxxxxxxxxx> wrote: > On Thu, Apr 21, 2011 at 10:00 PM, KAMEZAWA Hiroyuki < > kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > On Thu, 21 Apr 2011 21:49:04 -0700 > > Ying Han <yinghan@xxxxxxxxxx> wrote: > > > > > On Thu, Apr 21, 2011 at 9:36 PM, KAMEZAWA Hiroyuki < > > > kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > > > > > > On Thu, 21 Apr 2011 21:24:15 -0700 > > > > Ying Han <yinghan@xxxxxxxxxx> wrote: > > > > > > > > > This patch creates a thread pool for memcg-kswapd. All memcg which > > needs > > > > > background recalim are linked to a list and memcg-kswapd picks up a > > memcg > > > > > from the list and run reclaim. > > > > > > > > > > The concern of using per-memcg-kswapd thread is the system overhead > > > > including > > > > > memory and cputime. > > > > > > > > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > > > > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> > > > > > > > > Thank you for merging. This seems ok to me. > > > > > > > > Further development may make this better or change thread pools (to > > some > > > > other), > > > > but I think this is enough good. > > > > > > > > > > Thank you for reviewing and Acking. At the same time, I do have wondering > > on > > > the thread-pool modeling which I posted on the cover-letter :) > > > > > > The per-memcg-per-kswapd model > > > Pros: > > > 1. memory overhead per thread, and The memory consumption would be > > 8k*1000 = > > > 8M > > > with 1k cgroup. > > > 2. we see lots of threads at 'ps -elf' > > > > > > Cons: > > > 1. the implementation is simply and straigh-forward. > > > 2. we can easily isolate the background reclaim overhead between cgroups. > > > 3. better latency from memory pressure to actual start reclaiming > > > > > > The thread-pool model > > > Pros: > > > 1. there is no isolation between memcg background reclaim, since the > > memcg > > > threads > > > are shared. > > > 2. it is hard for visibility and debugability. I have been experienced a > > lot > > > when > > > some kswapds running creazy and we need a stright-forward way to identify > > > which > > > cgroup causing the reclaim. > > > 3. potential starvation for some memcgs, if one workitem stucks and the > > rest > > > of work > > > won't proceed. > > > > > > Cons: > > > 1. save some memory resource. > > > > > > In general, the per-memcg-per-kswapd implmentation looks sane to me at > > this > > > point, esepcially the sharing memcg thread model will make debugging > > issue > > > very hard later. > > > > > > Comments? > > > > > Pros <-> Cons ? > > > > My idea is adding trace point for memcg-kswapd and seeing what it's now > > doing. > > (We don't have too small trace point in memcg...) > > > > I don't think its sane to create kthread per memcg because we know there is > > a user > > who makes hundreds/thousands of memcg. > > > > And, I think that creating threads, which does the same job, more than the > > number > > of cpus will cause much more difficult starvation, priority inversion > > issue. > > Keeping scheduling knob/chances of jobs in memcg is important. I don't want > > to > > give a hint to scheduler because of memcg internal issue. > > > > And, even if memcg-kswapd doesn't exist, memcg works (well?). > > memcg-kswapd just helps making things better but not do any critical jobs. > > So, it's okay to have this as best-effort service. > > Of course, better scheduling idea for picking up memcg is welcomed. It's > > now > > round-robin. > > > > Hmm. The concern I have is the debug-ability. Let's say I am running a > system and found memcg-3 running crazy. Is there a way to find out which > memcg it is trying to reclaim pages from? Also, how to count cputime for the > shared memcg to the memcgs if we wanted to. > add a counter for kswapd-scan and kswapd-reclaim, kswapd-pickup will show you information, if necessary it's good to show some latecy stat. I think we can add enough information by adding stats (or debug by perf tools.) I'll consider this a a bit more. Thanks, -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>