From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754467AbdBVIt6 (ORCPT ); Wed, 22 Feb 2017 03:49:58 -0500 Received: from mx2.suse.de ([195.135.220.15]:43794 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753587AbdBVItt (ORCPT ); Wed, 22 Feb 2017 03:49:49 -0500 Date: Wed, 22 Feb 2017 09:49:47 +0100 From: Michal Hocko To: Wei Yang , Andrew Morton Cc: 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: <20170222084947.GE5753@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170209135929.GA59297@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 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. -- Michal Hocko SUSE Labs