On Wed, Aug 31, 2011 at 11:05:51PM -0700, Ying Han wrote: > On Tue, Aug 30, 2011 at 1:42 AM, Johannes Weiner <jweiner@xxxxxxxxxx> wrote: > > You want to look at A and see whether its limit was responsible for > > reclaim scans in any children. IMO, that is asking the question > > backwards. Instead, there is a cgroup under reclaim and one wants to > > find out the cause for that. Not the other way round. > > > > In my original proposal I suggested differentiating reclaim caused by > > internal pressure (due to own limit) and reclaim caused by > > external/hierarchical pressure (due to limits from parents). > > > > If you want to find out why C is under reclaim, look at its reclaim > > statistics. If the _limit numbers are high, C's limit is the problem. > > If the _hierarchical numbers are high, the problem is B, A, or > > physical memory, so you check B for _limit and _hierarchical as well, > > then move on to A. > > > > Implementing this would be as easy as passing not only the memcg to > > scan (victim) to the reclaim code, but also the memcg /causing/ the > > reclaim (root_mem): > > > > root_mem == victim -> account to victim as _limit > > root_mem != victim -> account to victim as _hierarchical > > > > This would make things much simpler and more natural, both the code > > and the way of tracking down a problem, IMO. > > This is pretty much the stats I am currently using for debugging the > reclaim patches. For example: > > scanned_pages_by_system 0 > scanned_pages_by_system_under_hierarchy 50989 > > scanned_pages_by_limit 0 > scanned_pages_by_limit_under_hierarchy 0 > > "_system" is count under global reclaim, and "_limit" is count under > per-memcg reclaim. > "_under_hiearchy" is set if memcg is not the one triggering pressure. I don't get this distinction between _system and _limit. How is it orthogonal to _limit vs. _hierarchy, i.e. internal vs. external? If the system scans memcgs then no limit is at fault. It's just external pressure. For example, what is the distinction between scanned_pages_by_system and scanned_pages_by_system_under_hierarchy? The reason for scanned_pages_by_system would be, per your definition, neither due to the limit (_by_system -> global reclaim) nor not due to the limit (!_under_hierarchy -> memcg is the one triggering pressure) -- 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>