linux-kernel - Re: [PATCH] memcg: Add memory.pressure

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Date:	Tue, 12 Feb 2013 23:19:22 -0800
From:	Anton Vorontsov <anton@...msg.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	cgroups@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH] memcg: Add memory.pressure_level events

Hi Glauber,

On Mon, Feb 11, 2013 at 02:17:06PM +0400, Glauber Costa wrote:
[...]
> > +static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
> > +{
> > +	struct cgroup *cg = vmpr_to_css(vmpr)->cgroup->parent;
> > +
> > +	if (!cg)
> > +		return NULL;
> > +	return cg_to_vmpr(cg);
> > +}
> 
> Unfortunately, "parent" in memcg have different meanings for information
> propagation purposes depending on the value of the flag "use_hierarchy".
> That is set for deprecation, but still...
> 
> I suggest you use the helper mem_cgroup_parent, that will already give
> you the right parent (either immediate parent or root) with all that
> taken into account.

Got it, will change.

[...]
> > +void __init enable_pressure_cgroup(void)
> > +{
> > +	WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
> > +				   vmpressure_cgroup_files));
> > +}
> 
> There is no functionality discovery going on here, and this is
> conditional on nothing. Isn't it better then to just add the register +
> read functions to memcontrol.c and add the files in the memcontrol cftype ?

I was trying to make the stuff similar to the existing CONFIG_MEMCG_SWAP
code, which does this kind of adding files to the cgroup. But I can surely
place files into memcontrol cftype as you suggest.

Thanks a lot for the comments!

Anton
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