Messages in this thread | | | Date | Sun, 20 Apr 2008 13:46:37 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][-mm] Memory controller hierarchy support (v1) |
| |
Paul Menage wrote: > On Fri, Apr 18, 2008 at 10:35 PM, Balbir Singh > <balbir@linux.vnet.ibm.com> wrote: >> 1. We need to hold cgroup_mutex while walking through the children >> in reclaim. We need to figure out the best way to do so. Should >> cgroups provide a helper function/macro for it? > > There's already a function, cgroup_lock(). But it would be nice to > avoid such a heavy locking here, particularly since memory allocations > can occur with cgroup_mutex held, which could lead to a nasty deadlock > if the allocation triggered reclaim. >
Hmm.. probably..
> One of the things that I've been considering was to put the > parent/child/sibling hierarchy explicitly in cgroup_subsys_state. This > would give subsystems their own copy to refer to, and could use their > own internal locking to synchronize with callbacks from cgroups that > might change the hierarchy. Cpusets could make use of this too, since > it has to traverse hierarchies sometimes. >
Very cool! I look forward to that infrastructure. I'll also look at the cpuset code and see how to traverse the hierarchy.
>> 2. Do not allow children to have a limit greater than their parents. >> 3. Allow the user to select if hierarchial support is required > > My thoughts on this would be: > > 1) Never attach a first-level child's counter to its parent. As > Yamamoto points out, otherwise we end up with extra global operations > whenever any cgroup allocates or frees memory. Limiting the total > system memory used by all user processes doesn't seem to be something > that people are going to generally want to do, and if they really do > want to they can just create a non-root child and move the whole > system into that. > > The one big advantage that you currently get from having all > first-level children be attached to the root is that the reclaim logic > automatically scans other groups when it reaches the top-level - but I > think that can be provided as a special-case in the reclaim traversal, > avoiding the overhead of hitting the root cgroup that we have in this > patch. >
I've been doing some thinking along these lines, I'll think more about this.
> 2) Always attach other children's counters to their parents - if the > user didn't want a hierarchy, they could create a flat grouping rather > than nested groupings. >
Yes, that's a TODO
> Paul
-- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL
| |