Messages in this thread | | | Date | Thu, 28 Jun 2012 17:33:51 +0900 | From | Kamezawa Hiroyuki <> | Subject | Re: [PATCH v3][0/6] memcg: prevent -ENOMEM in pre_destroy() |
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(2012/06/28 2:58), Tejun Heo wrote: > Hello, KAME. > > On Fri, Jun 22, 2012 at 08:27:25AM +0900, Kamezawa Hiroyuki wrote: >> Remaining 20% of work is based on a modification to cgroup layer >> >> How do you think this patch ? (This patch is not tested yet...so >> may have troubles...) I think callers of pre_destory() is not so many... >> >> == >> From a28db946f91f3509d25779e8c5db249506cc4b07 Mon Sep 17 00:00:00 2001 >> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> >> Date: Fri, 22 Jun 2012 08:38:38 +0900 >> Subject: [PATCH] cgroup: keep cgroup_mutex() while calling ->pre_destroy() >> >> In past, memcg's pre_destroy() was verrry slow because of the possibility >> of page reclaiming in it. So, cgroup_mutex() was released before calling >> pre_destroy() callbacks. Now, it's enough fast. memcg just scans the list >> and move pages to other cgroup, no memory reclaim happens. >> Then, we can keep cgroup_mutex() there. >> >> By holding looks, we can avoid following cases >> 1. new task is attached while rmdir(). >> 2. new child cgroup is created while rmdir() >> 3. new task is attached to cgroup and removed from cgroup before >> checking css's count. So, ->destroy() will be called even if >> some trashes by the task remains >> >> (3. is terrible case...even if I think it will not happen in real world..) > > Ooh, once memcg drops the __DEPRECATED_clear_css_refs, cgroup_rmdir() > will mark the cgroup dead before start calling pre_destroy() and none > of the above will happen. >
Hm, threads which touches memcg should hold memcg's reference count rather than css. Right ? IIUC, one of reason is a reference from kswapd etc...hm. I'll check it.
Thanks, -Kame
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