From: Li Zefan <lizf@cn.fujitsu.com>
To: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>,
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 15:31:03 +0800 [thread overview]
Message-ID: <4F17C6B7.5020606@cn.fujitsu.com> (raw)
In-Reply-To: <alpine.LSU.2.00.1201182155480.7862@eggly.anvils>
Hugh Dickins wrote:
> Commit c1e2ee2dc436 "memcg: replace ss->id_lock with a rwlock" has
> now been seen to cause the unfair behavior we should have expected
> from converting a spinlock to an rwlock: softlockup in cgroup_mkdir(),
> whose get_new_cssid() is waiting for the wlock, while there are 19
> tasks using the rlock in css_get_next() to get on with their memcg
> workload (in an artificial test, admittedly). Yet lib/idr.c was
> made suitable for RCU way back.
>
> 1. Revert that commit, restoring ss->id_lock to a spinlock.
>
> 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. Remove lock and unlock around css_get_next()'s call to idr_get_next():
> memcg iterators (only users of css_get_next) already did rcu_read_lock(),
> and comment demands that, but add a WARN_ON_ONCE to make sure of it.
>
> Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
>
> include/linux/cgroup.h | 2 +-
> kernel/cgroup.c | 19 +++++++++----------
> lib/idr.c | 4 ++--
> 3 files changed, 12 insertions(+), 13 deletions(-)
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next prev parent reply other threads:[~2012-01-19 7:28 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 [this message]
2012-01-19 7:33 ` Eric Dumazet
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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