On Thu, 5 May 2011 08:59:01 +0200 Michal Hocko <mhocko@xxxxxxx> wrote: > On Wed 04-05-11 10:16:39, Ying Han wrote: > > On Wed, May 4, 2011 at 1:58 AM, Michal Hocko <mhocko@xxxxxxx> wrote: > > > On Tue 03-05-11 10:01:27, Ying Han wrote: > > >> On Tue, May 3, 2011 at 1:25 AM, Michal Hocko <mhocko@xxxxxxx> wrote: > > >> > On Tue 03-05-11 16:45:23, KOSAKI Motohiro wrote: > > >> >> 2011/5/3 Michal Hocko <mhocko@xxxxxxx>: > > >> >> > On Sun 01-05-11 15:06:02, KOSAKI Motohiro wrote: > > >> >> >> > On Mon 25-04-11 18:28:49, KAMEZAWA Hiroyuki wrote: > > > [...] > > >> >> >> Can you please clarify this? I feel it is not opposite semantics. > > >> >> > > > >> >> > In the global reclaim low watermark represents the point when we _start_ > > >> >> > background reclaim while high watermark is the _stopper_. Watermarks are > > >> >> > based on the free memory while this proposal makes it based on the used > > >> >> > memory. > > >> >> > I understand that the result is same in the end but it is really > > >> >> > confusing because you have to switch your mindset from free to used and > > >> >> > from under the limit to above the limit. > > >> >> > > >> >> Ah, right. So, do you have an alternative idea? > > >> > > > >> > Why cannot we just keep the global reclaim semantic and make it free > > >> > memory (hard_limit - usage_in_bytes) based with low limit as the trigger > > >> > for reclaiming? > > >> > > > [...] > > >> The current scheme > > > > > > What is the current scheme? > > > > using the "usage_in_bytes" instead of "free" > > > > >> is closer to the global bg reclaim which the low is triggering reclaim > > >> and high is stopping reclaim. And we can only use the "usage" to keep > > >> the same API. > Sorry for long absence. > And how is this closer to the global reclaim semantic which is based on > the available memory? It's never be the same feature and not a similar feature, I think. > What I am trying to say here is that this new watermark concept doesn't > fit in with the global reclaim. Well, standard user might not be aware > of the zone watermarks at all because they cannot be set. But still if > you are analyzing your memory usage you still check and compare free > memory to min/low/high watermarks to find out what is the current memory > pressure. > If we had another concept with cgroups you would need to switch your > mindset to analyze things. > > I am sorry, but I still do not see any reason why those cgroup watermaks > cannot be based on total-usage. Hmm, so, the interface should be memory.watermark --- the total usage which kernel's memory shrinker starts. ? I'm okay with this. And I think this parameter should be fully independent from the limit. Memcg can work without watermark reclaim. I think my patch just adds a new _limit_ which a user can shrink usage of memory on deamand with kernel's help. Memory reclaim works in background but this is not a kswapd, at all. I guess performance benefit of using watermark under a cgroup which has limit is very small and I think this is not for a performance tuning parameter. This is just a new limit. Comparing 2 cases, cgroup A) - has limit of 300M, no watermaks. cgroup B) - has limit of UNLIMITED, watermarks=300M A) has hard limit and memory reclaim cost is paid by user threads, and have risks of OOM under memcg. B) has no hard limit and memory reclaim cost is paid by kernel threads, and will not have risk of OOM under memcg, but can be CPU burning. I think this should be called as soft-limit ;) But we have another soft-limit now. Then, I call this as watermark. This will be useful to resize usage of memory in online because application will not hit limit and get big latency even while an admin makes watermark smaller. Hmm, maybe I should allow watermark > limit setting ;). Thanks, -Kame 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>