From: Eric Dumazet <eric.dumazet@gmail.com>
To: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>, Li Zefan <lizf@cn.fujitsu.com>,
Andrew Morton <akpm@linux-foundation.org>,
Manfred Spraul <manfred@colorfullife.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Ying Han <yinghan@google.com>, Greg Thelen <gthelen@google.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next
Date: Thu, 19 Jan 2012 08:33:21 +0100 [thread overview]
Message-ID: <1326958401.1113.22.camel@edumazet-laptop> (raw)
In-Reply-To: <alpine.LSU.2.00.1201182155480.7862@eggly.anvils>
Le mercredi 18 janvier 2012 A 22:05 -0800, Hugh Dickins a A(C)crit :
> 2. Make one small adjustment to idr_get_next(): take the height from
> the top layer (stable under RCU) instead of from the root (unprotected
> by RCU), as idr_find() does.
>
> --- 3.2.0+/lib/idr.c 2012-01-04 15:55:44.000000000 -0800
> +++ linux/lib/idr.c 2012-01-18 21:25:36.947963342 -0800
> @@ -605,11 +605,11 @@ void *idr_get_next(struct idr *idp, int
> int n, max;
>
> /* find first ent */
> - n = idp->layers * IDR_BITS;
> - max = 1 << n;
> p = rcu_dereference_raw(idp->top);
> if (!p)
> return NULL;
> + n = (p->layer + 1) * IDR_BITS;
> + max = 1 << n;
>
> while (id < max) {
> while (n > 0 && p) {
Interesting, but should be a patch on its own.
Maybe other idr users can benefit from your idea as well, if patch is
labeled "idr: allow idr_get_next() from rcu_read_lock" or something...
I suggest introducing idr_get_next_rcu() helper to make the check about
rcu cleaner.
idr_get_next_rcu(...)
{
WARN_ON_ONCE(!rcu_read_lock_held());
return idr_get_next(...);
}
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next prev parent reply other threads:[~2012-01-19 7:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-19 6:05 Hugh Dickins
2012-01-19 6:58 ` KAMEZAWA Hiroyuki
2012-01-19 7:31 ` Li Zefan
2012-01-19 7:33 ` Eric Dumazet [this message]
2012-01-19 12:28 ` Tejun Heo
2012-01-19 13:30 ` Eric Dumazet
2012-01-19 20:46 ` Hugh Dickins
2012-01-19 20:48 ` [PATCH 1/3] idr: make idr_get_next() good for rcu_read_lock() Hugh Dickins
2012-01-20 23:48 ` Andrew Morton
2012-01-21 3:45 ` Hugh Dickins
2012-01-21 20:43 ` Randy Dunlap
2012-01-19 20:50 ` [PATCH 2/3] cgroup: revert ss_id_lock to spinlock Hugh Dickins
2012-01-19 20:51 ` [PATCH 3/3] memcg: let css_get_next() rely upon rcu_read_lock() Hugh Dickins
2012-01-19 20:53 ` Tejun Heo
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