From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qa0-f45.google.com (mail-qa0-f45.google.com [209.85.216.45]) by kanga.kvack.org (Postfix) with ESMTP id 29F286B0036 for ; Fri, 1 Aug 2014 13:16:58 -0400 (EDT) Received: by mail-qa0-f45.google.com with SMTP id cm18so4221082qab.32 for ; Fri, 01 Aug 2014 10:16:57 -0700 (PDT) Received: from USMAMAIL.TILERA.COM (usmamail.tilera.com. [12.216.194.151]) by mx.google.com with ESMTPS id n5si16602402qco.32.2014.08.01.10.16.57 for (version=TLSv1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 01 Aug 2014 10:16:57 -0700 (PDT) Message-ID: <53DBCB55.3050302@tilera.com> Date: Fri, 1 Aug 2014 13:16:05 -0400 From: Chris Metcalf MIME-Version: 1.0 Subject: Re: [PATCH] swap: remove the struct cpumask has_work References: <1406777421-12830-3-git-send-email-laijs@cn.fujitsu.com> <20140731115137.GA20244@dhcp22.suse.cz> <53DA6A2F.100@tilera.com> <53DAEFB5.7060501@cn.fujitsu.com> In-Reply-To: <53DAEFB5.7060501@cn.fujitsu.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Lai Jiangshan Cc: Michal Hocko , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Mel Gorman , Tejun Heo , Christoph Lameter , Frederic Weisbecker , Andrea Arcangeli , Rik van Riel , Jianyu Zhan , Johannes Weiner , Khalid Aziz , linux-mm@kvack.org, Gilad Ben-Yossef On 7/31/2014 9:39 PM, Lai Jiangshan wrote: > On 08/01/2014 12:09 AM, Chris Metcalf wrote: >> On 7/31/2014 7:51 AM, Michal Hocko wrote: >>> On Thu 31-07-14 11:30:19, Lai Jiangshan wrote: >>>> It is suggested that cpumask_var_t and alloc_cpumask_var() should be used >>>> instead of struct cpumask. But I don't want to add this complicity nor >>>> leave this unwelcome "static struct cpumask has_work;", so I just remove >>>> it and use flush_work() to perform on all online drain_work. flush_work() >>>> performs very quickly on initialized but unused work item, thus we don't >>>> need the struct cpumask has_work for performance. >>> Why? Just because there is general recommendation for using >>> cpumask_var_t rather than cpumask? >>> >>> In this particular case cpumask shouldn't matter much as it is static. >>> Your code will work as well, but I do not see any strong reason to >>> change it just to get rid of cpumask which is not on stack. >> The code uses for_each_cpu with a cpumask to avoid waking cpus that don't >> need to do work. This is important for the nohz_full type functionality, >> power efficiency, etc. So, nack for this change. >> > flush_work() on initialized but unused work item just disables irq and > fetches work->data to test and restores irq and return. > > the struct cpumask has_work is just premature optimization. Yes, I see your point. I was mistakenly thinking that your patch resulted in calling schedule_work() on all the online cpus. Given that, I think your suggestion is reasonable, though like Michal, I'm not sure it necessarily rises to the level of it being worth changing the code at this point. Regardless, I withdraw my nack, and you can add my Reviewed-by: Chris Metcalf if the change is taken. -- Chris Metcalf, Tilera Corp. http://www.tilera.com -- 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