From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933050AbcITPr0 (ORCPT ); Tue, 20 Sep 2016 11:47:26 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:33554 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932124AbcITPrY (ORCPT ); Tue, 20 Sep 2016 11:47:24 -0400 Date: Tue, 20 Sep 2016 17:47:20 +0200 From: Piotr Kwapulinski To: Michal Hocko Cc: akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, vbabka@suse.cz, rientjes@google.com, mgorman@techsingularity.net, liangchen.linux@gmail.com, nzimmer@sgi.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mempolicy.c: forbid static or relative flags for local NUMA mode Message-ID: <20160920154719.GA3899@home> References: <20160918112943.1645-1-kwapulinski.piotr@gmail.com> <20160919115204.GL10785@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160919115204.GL10785@dhcp22.suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 19, 2016 at 01:52:05PM +0200, Michal Hocko wrote: > On Sun 18-09-16 13:29:43, Piotr Kwapulinski wrote: > > The MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES flags are irrelevant > > when setting them for MPOL_LOCAL NUMA memory policy via set_mempolicy. > > Return the "invalid argument" from set_mempolicy whenever > > any of these flags is passed along with MPOL_LOCAL. > > man 2 set_mempolicy doesn't list this as invalid option. Maybe this is a > documentation bug but is it possible that somebody will see this as an > unexpected error? > The MPOL_LOCAL is currently not documented in "man set_mempolicy(2)". In case the nodemask is empty for MPOL_LOCAL it is transformed into MPOL_PREFERRED. The motivation for disabling MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES flags for MPOL_PREFERRED with empty nodemask is described at this commit 3e1f064562fcff7. Currently I call set_mempolicy(MPOL_LOCAL, ...) via the syscall() but despite of that it is inconsistent with MPOL_PREFERRED. > > It is consistent with MPOL_PREFERRED passed with empty nodemask. > > It also slightly shortens the execution time in paths where these flags > > are used e.g. when trying to rebind the NUMA nodes for changes in > > cgroups cpuset mems (mpol_rebind_preferred()) or when just printing > > the mempolicy structure (/proc/PID/numa_maps). > > I am not sure I understand this argument. What does this patch actually > fix? If this is about the execution time then why not just bail out > early when MPOL_LOCAL && (MPOL_F_STATIC_NODES || MPOL_F_RELATIVE_NODES) > The mpol_new() performs additional checks on nodemask. > > Isolated tests done. > > > > Signed-off-by: Piotr Kwapulinski > > --- > > mm/mempolicy.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > index 2da72a5..27b07d1 100644 > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -276,7 +276,9 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags, > > return ERR_PTR(-EINVAL); > > } > > } else if (mode == MPOL_LOCAL) { > > - if (!nodes_empty(*nodes)) > > + if (!nodes_empty(*nodes) || > > + (flags & MPOL_F_STATIC_NODES) || > > + (flags & MPOL_F_RELATIVE_NODES)) > > return ERR_PTR(-EINVAL); > > mode = MPOL_PREFERRED; > > } else if (nodes_empty(*nodes)) > > -- > > 2.9.2 > > -- > Michal Hocko > SUSE Labs -- Piotr Kwapulinski