From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753688AbcJMKoh (ORCPT ); Thu, 13 Oct 2016 06:44:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:50427 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751905AbcJMKo2 (ORCPT ); Thu, 13 Oct 2016 06:44:28 -0400 Date: Thu, 13 Oct 2016 11:24:59 +0100 From: Mel Gorman To: Michal Hocko Cc: Linux Kernel Mailing List , Linux Memory Management List , Andrew Morton , Anshuman Khandual , "Aneesh Kumar K.V" , Balbir Singh , Vlastimil Babka , Minchan Kim Subject: Re: MPOL_BIND on memory only nodes Message-ID: <20161013102459.GE20573@suse.de> References: <57FE0184.6030008@linux.vnet.ibm.com> <20161012094337.GH17128@dhcp22.suse.cz> <20161012131626.GL17128@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20161012131626.GL17128@dhcp22.suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 12, 2016 at 03:16:27PM +0200, Michal Hocko wrote: > On Wed 12-10-16 11:43:37, Michal Hocko wrote: > > On Wed 12-10-16 14:55:24, Anshuman Khandual wrote: > [...] > > > Why we insist on __GFP_THISNODE ? > > > > AFAIU __GFP_THISNODE just overrides the given node to the policy > > nodemask in case the current node is not part of that node mask. In > > other words we are ignoring the given node and use what the policy says. > > I can see how this can be confusing especially when confronting the > > documentation: > > > > * __GFP_THISNODE forces the allocation to be satisified from the requested > > * node with no fallbacks or placement policy enforcements. > > You made me think and look into this deeper. I came to the conclusion > that this is actually a relict from the past. policy_zonelist is called > only from 3 places: > - huge_zonelist - never should do __GFP_THISNODE when going this path > - alloc_pages_vma - which shouldn't depend on __GFP_THISNODE either > - alloc_pages_current - which uses default_policy id __GFP_THISNODE is > used > > So AFAICS this is essentially a dead code or I am missing something. Mel > do you remember why we needed it in the past? I don't recall a specific reason. It was likely due to confusion on my part at the time on the exact use of __GFP_THISNODE. The expectation is that flag is not used in fault paths or with policies. It's meant to enforce node-locality for kernel internal decisions such as the locality of slab pages and ensuring that a THP collapse from khugepaged is on the same node. -- Mel Gorman SUSE Labs