linux-kernel - Re: [PATCH 1/5] cgroup: ID notification call back

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Message-ID: <AANLkTi=imK6Px+JrdVupg2V3jtN9pgmEdWv=+aB1XKLY@mail.gmail.com>
Date:	Tue, 24 Aug 2010 17:09:25 -0700
From:	Paul Menage <menage@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	linux-mm@...ck.org,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	gthelen@...gle.com, m-ikeda@...jp.nec.com,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kamezawa.hiroyuki@...il.com,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>
Subject: Re: [PATCH 1/5] cgroup: ID notification call back

On Fri, Aug 20, 2010 at 2:58 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> CC'ed to Paul Menage and Li Zefan.
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> When cgroup subsystem use ID (ss->use_id==1), each css's ID is assigned
> after successful call of ->create(). css_ID is tightly coupled with
> css struct itself but it is allocated by ->create() call, IOW,
> per-subsystem special allocations.
>
> To know css_id before creation, this patch adds id_attached() callback.
> after css_ID allocation. This will be used by memory cgroup's quick lookup
> routine.
>
> Maybe you can think of other implementations as
>        - pass ID to ->create()
>        or
>        - add post_create()
>        etc...
> But when considering dirtiness of codes, this straightforward patch seems
> good to me. If someone wants post_create(), this patch can be replaced.

I think I'd prefer the approach where any necessary css_ids are
allocated prior to calling any create methods (which gives the
additional advantage of removing the need to roll back partial
creation of a cgroup in the event of alloc_css_id() failing) and then
passed in to the create() method. The main cgroups framework would
still be responsible for actually filling the css->id field with the
allocated id.

Paul
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