Messages in this thread | | | Date | Sun, 17 Aug 2008 09:15:39 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] cgroup: memory.force_empty can make system slowdown |
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IKEDA, Munehiro wrote: > Cgroup's memory controller has a control file "memory.force_empty" > to reset usage account charged to a cgroup. The account shouldn't > be reset if one or more processes are attached to the cgroup (at > least for memory controller, IMHO). So mem_cgroup_force_empty() > is implemented to return -EBUSY and do nothing if so. > However, cgroup on hierarchy root faultily might be a exception. > Even if processes are attached to root cgroup (which is a "default" > cgroup for processes), forcing-empty can run by writing something to > memory.force_empty and it'll never end. >
I found this bug last week, and I've made patches to fix it, but then I was on vacation. I'll send the patches out soon.
> Following patch prevents this issue. > > This patch is for cgroup infrastructure code. The issue can be > measured by modifying memory controller code also, namely to change > mem_cgroup_force_empty() to see CSS_ROOT bit of css->flags. > I believe cgroup->count approach like the patch below is rather > generic and reasonable, how does that sound? >
It's ok for the top_group's count to be 0 due to the top_cgroup hack. With this patch, the top cgroup's count will be always >0, even if it has no tasks in it, so writing to top_cgroup's force_empty will always return -EBUSY.
> Paul, Balbir? > > > > Signed-off-by: Munehiro "Muuhh" Ikeda <m-ikeda@ds.jp.nec.com> > > diff -uNrp linux-2.6.27-rc3.orig/kernel/cgroup.c linux-2.6.27-rc3/kernel/cgroup.c > --- linux-2.6.27-rc3.orig/kernel/cgroup.c 2008-08-12 21:55:39.000000000 -0400 > +++ linux-2.6.27-rc3/kernel/cgroup.c 2008-08-15 20:52:52.000000000 -0400 > @@ -2264,8 +2264,10 @@ static void init_cgroup_css(struct cgrou > css->cgroup = cgrp; > atomic_set(&css->refcnt, 0); > css->flags = 0; > - if (cgrp == dummytop) > + if (cgrp == dummytop) { > set_bit(CSS_ROOT, &css->flags); > + atomic_set(&css->cgroup->count, 1); > + } > BUG_ON(cgrp->subsys[ss->subsys_id]); > cgrp->subsys[ss->subsys_id] = css; > } > > >
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