Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751976AbbHMARP (ORCPT ); Wed, 12 Aug 2015 20:17:15 -0400 Received: from mail-pa0-f44.google.com ([209.85.220.44]:36064 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751843AbbHMAQz (ORCPT ); Wed, 12 Aug 2015 20:16:55 -0400 Date: Wed, 12 Aug 2015 17:16:50 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Mel Gorman cc: Linux-MM , Johannes Weiner , Rik van Riel , Vlastimil Babka , Joonsoo Kim , Michal Hocko , LKML Subject: Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled In-Reply-To: <1439376335-17895-5-git-send-email-mgorman@techsingularity.net> Message-ID: References: <1439376335-17895-1-git-send-email-mgorman@techsingularity.net> <1439376335-17895-5-git-send-email-mgorman@techsingularity.net> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1827 Lines: 53 On Wed, 12 Aug 2015, Mel Gorman wrote: > There is a seqcounter that protects against spurious allocation failures > when a task is changing the allowed nodes in a cpuset. There is no need > to check the seqcounter until a cpuset exists. > > Signed-off-by: Mel Gorman > Acked-by: David Rientjes > Acked-by: Vlastimil Babka > --- > include/linux/cpuset.h | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index 1b357997cac5..6eb27cb480b7 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct task_struct *p); > */ > static inline unsigned int read_mems_allowed_begin(void) > { > + if (!cpusets_enabled()) > + return 0; > + > return read_seqcount_begin(¤t->mems_allowed_seq); > } > > @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void) > */ > static inline bool read_mems_allowed_retry(unsigned int seq) > { > + if (!cpusets_enabled()) > + return false; > + > return read_seqcount_retry(¤t->mems_allowed_seq, seq); > } > This patch is an obvious improvement, but I think it's also possible to change this to be if (nr_cpusets() <= 1) return false; and likewise in the existing cpusets_enabled() check in get_page_from_freelist(). A root cpuset may not exclude mems on the system so, even if mounted, there's no need to check or be worried about concurrent change when there is only one cpuset. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/