Messages in this thread | | | Date | Thu, 22 Mar 2012 14:29:41 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] memcg: change behavior of moving charges at task move |
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On Wed, 21 Mar 2012 18:52:04 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> As discussed before, I post this to fix the spec and implementation of task moving. > Then, do you think what target kernel version should be ? 3.4/3.5 ? > but yes, it may be late for 3.4....
Well, the key information here is "what effect does the bug have upon users".
> In documentation, it's said that 'shared anon are not moved'. > But in implementation, the check was wrong. > > if (!move_anon() || page_mapcount(page) > 2) > > Ah, memcg has been moving shared anon pages for a long time. > > Then, here is a discussion about handling of shared anon pages. > > - It's complex > - Now, shared file caches are moved in force. > - It adds unclear check as page_mapcount(). To do correct check, > we should check swap users, etc. > - No one notice this implementation behavior. So, no one get benefit > from the design. > - In general, once task is moved to a cgroup for running, it will not > be moved.... > - Finally, we have control knob as memory.move_charge_at_immigrate. > > Here is a patch to allow moving shared pages, completely. This makes > memcg simpler and fix current broken code. > > Note: > IIUC, libcgroup's cgroup daemon moves tasks after exec(). > So, it's not affected. > libcgroup's command "cgexec" does move itsef to a memcg and call exec() > without fork(). it's not affected. > > Changelog: > - fixed PageAnon() check. > - remove call of lookup_swap_cache() > - fixed Documentation.
But you forgot to tell us :(
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