On Thu, Apr 21, 2011 at 02:41:56PM +0900, KAMEZAWA Hiroyuki wrote: > On Thu, 21 Apr 2011 07:08:51 +0200 > Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > On Thu, Apr 21, 2011 at 01:00:16PM +0900, KAMEZAWA Hiroyuki wrote: > > > On Thu, 21 Apr 2011 04:51:07 +0200 > > > Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > > > > > > > If the cgroup is configured to use per cgroup background reclaim, a kswapd > > > > > thread is created which only scans the per-memcg LRU list. > > > > > > > > We already have direct reclaim, direct reclaim on behalf of a memcg, > > > > and global kswapd-reclaim. Please don't add yet another reclaim path > > > > that does its own thing and interacts unpredictably with the rest of > > > > them. > > > > > > > > As discussed on LSF, we want to get rid of the global LRU. So the > > > > goal is to have each reclaim entry end up at the same core part of > > > > reclaim that round-robin scans a subset of zones from a subset of > > > > memory control groups. > > > > > > It's not related to this set. And I think even if we remove global LRU, > > > global-kswapd and memcg-kswapd need to do independent work. > > > > > > global-kswapd : works for zone/node balancing and making free pages, > > > and compaction. select a memcg vicitm and ask it > > > to reduce memory with regard to gfp_mask. Starts its work > > > when zone/node is unbalanced. > > > > For soft limit reclaim (which is triggered by global memory pressure), > > we want to scan a group of memory cgroups equally in round robin > > fashion. I think at LSF we established that it is not fair to find > > the one that exceeds its limit the most and hammer it until memory > > pressure is resolved or there is another group with more excess. > > > > Why do you guys like to make a mixture discussion of softlimit and > high/low watermarks ? I just tried to make the point that both have the same requirements and argued that it would make sense to go in a direction that benefits future work as well. > > > > Which brings me to the next issue: making the watermarks configurable. > > > > > > > > You argued that having them adjustable from userspace is required for > > > > overcommitting the hardlimits and per-memcg kswapd reclaim not kicking > > > > in in case of global memory pressure. But that is only a problem > > > > because global kswapd reclaim is (apart from soft limit reclaim) > > > > unaware of memory control groups. > > > > > > > > I think the much better solution is to make global kswapd memcg aware > > > > (with the above mentioned round-robin reclaim scheduler), compared to > > > > adding new (and final!) kernel ABI to avoid an internal shortcoming. > > > > > > I don't think its a good idea to kick kswapd even when free memory is enough. > > > > This depends on what kswapd is supposed to be doing. I don't say we > > should reclaim from all memcgs (i.e. globally) just because one memcg > > hits its watermark, of course. > > > > But the argument was that we need the watermarks configurable to force > > per-memcg reclaim even when the hard limits are overcommitted, because > > global reclaim does not do a fair job to balance memcgs. > > I cannot understand here. Why global reclaim need to do works other than > balancing zones ? And what is balancing memcg ? Mentioning softlimit ? By 'balancing memcgs' I mean equally distributing scan pressure amongst them. When global reclaim kicks in, it may reclaim much more from one memcg than from another by accident. I assume that the only reason for making watermarks configurable is that global reclaim sucks and that you want to force watermark-based reclaim even when overcommitting. Maybe I should stop making this assumption and ask you for a good explanation of why you want to make watermarks configurable. > Hi/Low watermak is a feature as it is. It the 3rd way to limit memory > usage. Comaparing hard_limit, soft_limit, it works in moderate way in background > and works regardless of usage of global memory. I think it's valid to have > ineterfaces to tuning this. Can you elaborate more on this? I don't see your argument for it. Thanks, Hannes -- 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>