From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx109.postini.com [74.125.245.109]) by kanga.kvack.org (Postfix) with SMTP id E625A6B004F for ; Thu, 19 Jan 2012 02:33:25 -0500 (EST) Received: by wicr5 with SMTP id r5so5827560wic.14 for ; Wed, 18 Jan 2012 23:33:24 -0800 (PST) Message-ID: <1326958401.1113.22.camel@edumazet-laptop> Subject: Re: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next From: Eric Dumazet Date: Thu, 19 Jan 2012 08:33:21 +0100 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Tejun Heo , Li Zefan , Andrew Morton , Manfred Spraul , KAMEZAWA Hiroyuki , Johannes Weiner , Ying Han , Greg Thelen , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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(...); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org