linux-kernel - Re: [PATCH 6/9] cgroup_freezer: make freezer->state mask of flags

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Message-ID: <20121108143853.GC12973@htj.dyndns.org>
Date:	Thu, 8 Nov 2012 06:38:53 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	lizefan@...wei.com, mhocko@...e.cz, rjw@...k.pl,
	linux-pm@...r.kernel.org, fweisbec@...il.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 6/9] cgroup_freezer: make freezer->state mask of flags

Hello, Kamezawa.

On Thu, Nov 08, 2012 at 02:00:34PM +0900, Kamezawa Hiroyuki wrote:
> (2012/11/08 13:42), Tejun Heo wrote:
> >Hello, Kame.
> >
> >On Thu, Nov 08, 2012 at 01:37:50PM +0900, Kamezawa Hiroyuki wrote:
> >>How about
> >>enum {
> >>    __CGROUP_FREEZING,
> >>    __CGROUP_FROZEN,
> >>};
> >>
> >>#define CGROUP_FREEZER_STATE_MASK  0x3
> >>#define CGROUP_FREEZER_STATE(state)	((state) & CGROUP_FREEZER_STATE_MASK)
> >>#define CGROUP_THAW(state)	(CGROUP_FREEZER_STATE(state) == 0)
> >>#define CGROUP_FREEZING(state)	(CGROUP_FREEZER_STATE(state) == __CGROUP_FREEZING)
> >>#define CGROUP_FROZEN(state)\
> >>	(CGROUP_FREEZER_STATE(state) == (__CGROUP_FREEZING | __CGROUP_FROZEN))
> >
> >I think it's a bit overdone and we have cases where we test for
> >FREEZING regardless of FROZEN and cases where test for FREEZING &&
> >!FROZEN.  We can have, say, CGROUP_FREZING() and then
> >CGROUP_FREEZING_BUT_NOT_FROZEN(), but it feels more like obfuscation
> >than anything else.
> >
> 
> Hm, then, I'm glad if I can see what combinations of flags are valid and
> meanings of them in source code comments.

Ooh, the following comment is added by a later patch when the whole
thing is complete.

/*
 * A cgroup is freezing if any FREEZING flags are set.  FREEZING_SELF is
 * set if "FROZEN" is written to freezer.state cgroupfs file, and cleared
 * for "THAWED".  FREEZING_PARENT is set if the parent freezer is FREEZING
 * for whatever reason.  IOW, a cgroup has FREEZING_PARENT set if one of
 * its ancestors has FREEZING_SELF set.
 */

Thanks.

-- 
tejun
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