Messages in this thread | | | Date | Wed, 12 Nov 2008 17:04:00 -0800 | From | Andrew Morton <> | Subject | Re: [RFC][PATCH 1/6] memcg: free all at rmdir |
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On Thu, 13 Nov 2008 06:18:56 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> Andrew Morton wrote: > > On Thu, 13 Nov 2008 05:53:49 +0530 > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > >> Andrew Morton wrote: > >>> On Wed, 12 Nov 2008 12:26:56 +0900 > >>> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > >>> > >>>> +5.1 on_rmdir > >>>> +set behavior of memcg at rmdir (Removing cgroup) default is "drop". > >>>> + > >>>> +5.1.1 drop > >>>> + #echo on_rmdir drop > memory.attribute > >>>> + This is default. All pages on the memcg will be freed. > >>>> + If pages are locked or too busy, they will be moved up to the parent. > >>>> + Useful when you want to drop (large) page caches used in this memcg. > >>>> + But some of in-use page cache can be dropped by this. > >>>> + > >>>> +5.1.2 keep > >>>> + #echo on_rmdir keep > memory.attribute > >>>> + All pages on the memcg will be moved to its parent. > >>>> + Useful when you don't want to drop page caches used in this memcg. > >>>> + You can keep page caches from some library or DB accessed by this > >>>> + memcg on memory. > >>> Would it not be more useful to implement a per-memcg version of > >>> /proc/sys/vm/drop_caches? (One without drop_caches' locking bug, > >>> hopefully). > >>> > >>> If we do this then we can make the above "keep" behaviour non-optional, > >>> and the operator gets to choose whether or not to drop the caches > >>> before doing the rmdir. > >>> > >>> Plus, we get a new per-memcg drop_caches capability. And it's a nicer > >>> interface, and it doesn't have the obvious races which on_rmdir has, > >>> etc. > >>> > >> Andrew, I suspect that will not be easy, since we don't track address spaces > >> that belong to a particular memcg. If page cache ends up being shared across > >> memcg's, dropping them would impact both mem cgroups. > >> > > > > walk the LRUs? > > We do that for the force_empty() interface we have. Although we don't > differentiate between cache and RSS at the moment.
so.. what's wrong with using that (possibly with some generalisation/enhancement)?
btw, mem_cgroup_force_empty_list() uses PageLRU() outside ->lru_lock. That's racy, although afaict this race will only cause an accounting error.
Or maybe not. What happens if __mem_cgroup_uncharge_common()->__mem_cgroup_remove_list() is passed a page which isn't on an LRU any more? boom?
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