From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f43.google.com (mail-pa0-f43.google.com [209.85.220.43]) by kanga.kvack.org (Postfix) with ESMTP id 7C1476B0038 for ; Wed, 12 Aug 2015 20:16:55 -0400 (EDT) Received: by pawu10 with SMTP id u10so24880388paw.1 for ; Wed, 12 Aug 2015 17:16:55 -0700 (PDT) Received: from mail-pa0-x234.google.com (mail-pa0-x234.google.com. [2607:f8b0:400e:c03::234]) by mx.google.com with ESMTPS id qb10si680243pdb.150.2015.08.12.17.16.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 12 Aug 2015 17:16:54 -0700 (PDT) Received: by pacgr6 with SMTP id gr6so24763252pac.2 for ; Wed, 12 Aug 2015 17:16:54 -0700 (PDT) Date: Wed, 12 Aug 2015 17:16:50 -0700 (PDT) From: David Rientjes 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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linux-MM , Johannes Weiner , Rik van Riel , Vlastimil Babka , Joonsoo Kim , Michal Hocko , LKML 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, 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/ . Don't email: email@kvack.org