linux-kernel - Re: [PATCH 5/8] cgroup: remove CGRP_WAIT_ON_RMDIR, cgroup_exclude_rmdir() and cgroup_release_and_wakeup

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Date:	Fri, 02 Nov 2012 19:20:38 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	lizefan@...wei.com, hannes@...xchg.org, mhocko@...e.cz,
	bsingharora@...il.com, containers@...ts.linux-foundation.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] cgroup: remove CGRP_WAIT_ON_RMDIR, cgroup_exclude_rmdir()
 and cgroup_release_and_wakeup_rmdir()

(2012/11/01 4:44), Tejun Heo wrote:
> CGRP_WAIT_ON_RMDIR is another kludge which was added to make cgroup
> destruction rollback somewhat working.  cgroup_rmdir() used to drain
> CSS references and CGRP_WAIT_ON_RMDIR and the associated waitqueue and
> helpers were used to allow the task performing rmdir to wait for the
> next relevant event.
> 
> Unfortunately, the wait is visible to controllers too and the
> mechanism got exposed to memcg by 887032670d ("cgroup avoid permanent
> sleep at rmdir").
> 
> Now that the draining and retries are gone, CGRP_WAIT_ON_RMDIR is
> unnecessary.  Remove it and all the mechanisms supporting it.  Note
> that memcontrol.c changes are essentially revert of 887032670d
> ("cgroup avoid permanent sleep at rmdir").
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

plz forget my comments on v1...But...

If swap-in makes a charge before css is deactivated, pre_destroy()->force_empty()
will cause infinite loop until it finds a newly charged page in LRU. I think
force_empty() will find it by lru_drain() and can make res_coutnter to be 0.

I think we need some test with swap-in handling..Anyway, 

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>


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