Messages in this thread | | | Date | Wed, 10 Dec 2008 08:19:29 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][PATCH 4/6] Flat hierarchical reclaim by ID |
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2008-12-10 01:34:14]:
> Balbir Singh said: > > >> I think your soft-limit idea can be easily merged onto this patch > >> set. > >> > > > > Yes, potentially. With soft limit, the general expectation is this > > > > Let us say you have group A and B > > > > groupA, soft limit = 1G > > groupB, soft limit = 2G > > > > Now assume the system has 4G. When groupB is not using its memory, > > group A can grab all 4G, but when groupB kicks in and tries to use 2G > > or more, then the expectation is that > > > > group A will get 1/3 * 4 = 4/3G > > group B will get 2/3 * 4 = 8/3G > > > > Similar to CPU shares currently. > > > I like that idea because it's easy to understand. >
Excellent, I'll start looking at how to implement it
> >> > Does this order reflect their position in the hierarchy? > >> No. just scan IDs from last scannned one in RR. > >> BTW, can you show what an algorithm works well in following case ? > >> ex) > >> groupA/ limit=1G usage=300M > >> 01/ limit=600M usage=600M > >> 02/ limit=700M usage=70M > >> 03/ limit=100M usage=30M > >> Which one should be shrinked at first and why ? > >> 1) when group_A hit limits. > > > > With tree reclaim, reclaim will first reclaim from A and stop if > > successful, otherwise it will go to 01, 02 and 03 and then go back to > > A. > > > Sorry for my poor example > > >> 2) when group_A/01 hit limits. > > > > This will reclaim only from 01, since A is under its limit > > > I should ask > 2') when a task in group_A/01 hit limit in group_A > > ex) > group_A/ limtit=1G, usage~0 > /01 limit= unlimited usage=800M > /02 limit= unlimited usage=200M > (what limit is allowed to children is another problem to be fixed...) > when a task in 01 hits limit of group_A > when a task in 02 hits limit of group_A > where we should start from ? (is unknown) > Currenty , this patch uses RR (in A->01->02->A->...). > and soft-limit or some good algorithm will give us better view. > > >> 3) when group_A/02 hit limits. > > > > This will reclaim only from 02 since A is under its limit > > > > Does RR do the same right now? > > > I think so. > > Assume > group_A/ > /01 > /02 > RR does > 1) when a task under A/01/02 hit limits at A, shrink A, 01, 02, > 2) when a task under 01 hit limits at 01, shrink only 01. > 3) when a task under 02 hit limits at 02, shrink only 02. > > When 1), start point of shrinking is saved as last_scanned_child. > > > >> I can't now. > >> > >> This patch itself uses round-robin and have no special order. > >> I think implenting good algorithm under this needs some amount of > >> time. > >> > > > > I agree that fine tuning it will require time, but what we need is > > something usable that will not have hard to debug or understand corner > > cases. > > yes, we have now. My point is "cgroup_lock()" caused many problems and > will cause new ones in future, I convince. > > And please see 5/6 and 6/6 we need hierarchy consideration in other > places. I think there are more codes which should take care of hierarchy. >
Yes, I do have the patches to remove cgroup_lock(), let me post them indepedent of Daisuke's patches
> > > > Shouldn't id's belong to cgroups instead of just memory controller? > >> If Paul rejects, I'll move this to memcg. But bio-cgroup people also use > >> ID and, in this summer, I posted swap-cgroup-ID patch and asked to > >> implement IDs under cgroup rather than subsys. (asked by Paul or you.) > >> > > > > We should talk to Paul and convince him. > > > yes. >
Paul, would it be very hard to add id's to control groups?
> >> >From implementation, hierarchy code management at el. should go into > >> cgroup.c and it gives us clear view rather than implemented under memcg. > >> > > > > cgroup has hierarchy management already, in the form of children and > > sibling. Walking those structures is up to us, that is all we do > > currently :) > > > yes, but need cgroup_lock(). and you have to keep refcnt to pointer > just for rememebring it. > > This patch doesn't change anything other than removing cgroup_lock() and > removing refcnt to remember start point. >
OK, I'll play with it
-- Balbir
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