Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752721AbaBSIQr (ORCPT ); Wed, 19 Feb 2014 03:16:47 -0500 Received: from cantor2.suse.de ([195.135.220.15]:50499 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751480AbaBSIQq (ORCPT ); Wed, 19 Feb 2014 03:16:46 -0500 Date: Wed, 19 Feb 2014 09:16:44 +0100 From: Michal Hocko To: David Rientjes Cc: Anton Blanchard , Benjamin Herrenschmidt , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, LKML Subject: Re: ppc: RECLAIM_DISTANCE 10? Message-ID: <20140219081644.GA14783@dhcp22.suse.cz> References: <20140218090658.GA28130@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 18-02-14 14:27:11, David Rientjes wrote: > On Tue, 18 Feb 2014, Michal Hocko wrote: > > > Hi, > > I have just noticed that ppc has RECLAIM_DISTANCE reduced to 10 set by > > 56608209d34b (powerpc/numa: Set a smaller value for RECLAIM_DISTANCE to > > enable zone reclaim). The commit message suggests that the zone reclaim > > is desirable for all NUMA configurations. > > > > History has shown that the zone reclaim is more often harmful than > > helpful and leads to performance problems. The default RECLAIM_DISTANCE > > for generic case has been increased from 20 to 30 around 3.0 > > (32e45ff43eaf mm: increase RECLAIM_DISTANCE to 30). > > > > I strongly suspect that the patch is incorrect and it should be > > reverted. Before I will send a revert I would like to understand what > > led to the patch in the first place. I do not see why would PPC use only > > LOCAL_DISTANCE and REMOTE_DISTANCE distances and in fact machines I have > > seen use different values. > > > > I strongly suspect that the patch is correct since powerpc node distances > are different than the architectures you're talking about and get doubled > for every NUMA domain that the hardware supports. Even if the units of the distance is different on PPC should every NUMA machine have zone_reclaim enabled? That doesn't right to me. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/