From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932536AbdBVLpd (ORCPT ); Wed, 22 Feb 2017 06:45:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:55067 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932291AbdBVLpY (ORCPT ); Wed, 22 Feb 2017 06:45:24 -0500 Date: Wed, 22 Feb 2017 12:45:22 +0100 From: Michal Hocko To: Wei Yang Cc: Andrew Morton , vbabka@suse.cz, mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_alloc: return 0 in case this node has no page within the zone Message-ID: <20170222114521.GJ5753@dhcp22.suse.cz> References: <20170206154314.15705-1-richard.weiyang@gmail.com> <20170207094557.GE5065@dhcp22.suse.cz> <20170207153247.GB31837@WeideMBP.lan> <20170207154120.GW5065@dhcp22.suse.cz> <20170209135929.GA59297@WeideMacBook-Pro.local> <20170222084947.GE5753@dhcp22.suse.cz> <20170222105131.GA57616@WeideMacBook-Pro.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170222105131.GA57616@WeideMacBook-Pro.local> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 22-02-17 18:51:31, Wei Yang wrote: > On Wed, Feb 22, 2017 at 09:49:47AM +0100, Michal Hocko wrote: > >On Thu 09-02-17 21:59:29, Wei Yang wrote: > >> On Tue, Feb 07, 2017 at 04:41:21PM +0100, Michal Hocko wrote: > >> >On Tue 07-02-17 23:32:47, Wei Yang wrote: > >> >> On Tue, Feb 07, 2017 at 10:45:57AM +0100, Michal Hocko wrote: > >> >[...] > >> >> >Is there any reason why for_each_mem_pfn_range cannot be changed to > >> >> >honor the given start/end pfns instead? I can imagine that a small zone > >> >> >would see a similar pointless iterations... > >> >> > > >> >> > >> >> Hmm... No special reason, just not thought about this implementation. And > >> >> actually I just do the similar thing as in zone_spanned_pages_in_node(), in > >> >> which also return 0 when there is no overlap. > >> >> > >> >> BTW, I don't get your point. You wish to put the check in > >> >> for_each_mem_pfn_range() definition? > >> > > >> >My point was that you are handling one special case (an empty zone) but > >> >the underlying problem is that __absent_pages_in_range might be wasting > >> >cycles iterating over memblocks that are way outside of the given pfn > >> >range. At least this is my understanding. If you fix that you do not > >> >need the special case, right? > >> >-- > >> >Michal Hocko > >> >SUSE Labs > >> > >> > Not really, sorry, this area is full of awkward and subtle code when new > >> > changes build on top of previous awkwardness/surprises. Any cleanup > >> > would be really appreciated. That is the reason I didn't like the > >> > initial check all that much. > >> > >> Looks my fetchmail failed to get your last reply. So I copied it here. > >> > >> Yes, the change here looks not that nice, while currently this is what I can't > >> come up with. > > > >THen I will suggest dropping this patch from the mmotm tree because it > >doesn't sound like a big improvement and I would encourage you or > >anybody else to take a deeper look and unclutter this area to be more > >readable and better maintainable. > > Hi, Michal > > I don't get your point, which part of the code makes you feel uncomfortable? It adds a check which would better be handled at a different level. I've tried to explain what are my concerns about quick&dirty solutions in this area. I would agree to add the check as a immediate workaround if this had some measurable benefits but the changelog doesn't mention any. So I do not really see this as an improvement in the end. If we want to address the suboptimal code, let's do it properly rather than spewing ifs all over the code. -- Michal Hocko SUSE Labs