From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754932AbcJMMjY (ORCPT ); Thu, 13 Oct 2016 08:39:24 -0400 Received: from mail-lf0-f66.google.com ([209.85.215.66]:32944 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753441AbcJMMjS (ORCPT ); Thu, 13 Oct 2016 08:39:18 -0400 Date: Thu, 13 Oct 2016 14:38:46 +0200 From: Michal Hocko To: Mel Gorman 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: <20161013123846.GM21678@dhcp22.suse.cz> References: <57FE0184.6030008@linux.vnet.ibm.com> <20161012094337.GH17128@dhcp22.suse.cz> <20161012131626.GL17128@dhcp22.suse.cz> <20161013102459.GE20573@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161013102459.GE20573@suse.de> 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 13-10-16 11:24:59, Mel Gorman wrote: > 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. This is my understanding as well. Thanks for double checking. I will send a proper patch (it will even compile as a bonus point ;). -- Michal Hocko SUSE Labs