linux-kernel - Re: [PATCH 2/7] cgroups: New resource counter inheritance API

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Message-ID: <CAJniumXEPUkRpLdfnu3g-NPBH_mEKYmov1P6+6m3+SXh9sZCvA@mail.gmail.com>
Date:	Mon, 11 Jul 2011 13:41:31 -0700
From:	Paul Menage <menage@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>
Subject: Re: [PATCH 2/7] cgroups: New resource counter inheritance API

On Mon, Jul 11, 2011 at 7:15 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> Provide an API to inherit a counter value from a parent.
> This can be useful to implement cgroup.clone_children on
> a resource counter.
>
> Still the resources of the children are limited by those
> of the parent, so this is only to provide a default setting
> behaviour when clone_children is set.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Can't this be just:

void res_counter_inherit(struct res_counter *counter, int member) {
  struct res_counter *parent;
  parent = counter->parent;
  if (parent)
    res_counter_write_u64(counter, member,
res_counter_read_u64(parent, member));
}

This is just used at cgroup creation time, right? So the performance
impact of an extra cli/sti shouldn't matter.

Also, looking at the code res_counter_read_u64() appears to not do any
locking. I don't recall why I added it like that, but it probably
ought to do at least an atomic64_read().

Paul
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