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Message-ID: <20091211021405.GA10693@localhost>
Date: Fri, 11 Dec 2009 10:14:05 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc: Andi Kleen <andi@...stfloor.org>, Paul Menage <menage@...gle.com>,
"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"npiggin@...e.de" <npiggin@...e.de>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"Li, Haicheng" <haicheng.li@...el.com>
Subject: Re: [PATCH] [23/31] HWPOISON: add memory cgroup filter
On Thu, Dec 10, 2009 at 10:21:13AM +0800, Balbir Singh wrote:
> * Andi Kleen <andi@...stfloor.org> [2009-12-10 02:42:12]:
>
> > > While the functionality sounds useful, the interface (passing an inode
> > > number) feels a bit ugly to me. Also, if that group is deleted and a
> > > new cgroup created, you could end up reusing the inode number.
> >
> > Please note this is just a testing interface, doesn't need to be
> > 100% fool-proof. It'll never be used in production.
> >
> > >
> > > How about an approach where you write either the cgroup path (relative
> > > to the memcg mount) or an fd open on the desired cgroup? Then you
> > > could store a (counted) css reference rather than an inode number,
> > > which would make the filter function cleaner too, since it would just
> > > need to compare css objects.
> >
> > Sounds complicated, I assume it would be much more code?
> > I would prefer to keep the testing interfaces as simple as possible.
> >
>
> We do this for cgroupstats and the code is not very complicated. In
> case you want to look, the user space code is at
> Documentation/accounting/getdelays.c and the kernel code is in
> kernel/taskstats.c
Balbir, thanks for the tip.
We could keep an fd open on the desired cgroup, in user space:
#!/bin/bash
mkdir /cgroup/hwpoison && \
exec 9<>/cgroup/hwpoison/tasks || exit 1
A bit simpler than an in-kernel fget_light() or CSS refcount :)
Thanks,
Fengguang
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