From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e18.ny.us.ibm.com (e18.ny.us.ibm.com [129.33.205.208]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id A15CD1A0957 for ; Sat, 9 May 2015 09:19:01 +1000 (AEST) Received: from /spool/local by e18.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 8 May 2015 19:18:58 -0400 Received: from b01cxnp23034.gho.pok.ibm.com (b01cxnp23034.gho.pok.ibm.com [9.57.198.29]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id E62626E803C for ; Fri, 8 May 2015 19:10:43 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t48NItqF63242316 for ; Fri, 8 May 2015 23:18:55 GMT Received: from d01av02.pok.ibm.com (localhost [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t48NIrxp032520 for ; Fri, 8 May 2015 19:18:55 -0400 Date: Fri, 8 May 2015 16:18:52 -0700 From: Nishanth Aravamudan To: Andrew Morton Subject: Re: [PATCH v2] mm: vmscan: do not throttle based on pfmemalloc reserves if node has no reclaimable pages Message-ID: <20150508231852.GA53489@linux.vnet.ibm.com> References: <20150327192850.GA18701@linux.vnet.ibm.com> <5515BAF7.6070604@intel.com> <20150327222350.GA22887@linux.vnet.ibm.com> <20150331094829.GE9589@dhcp22.suse.cz> <551E47EF.5030800@suse.cz> <20150403174556.GF32318@linux.vnet.ibm.com> <20150505220913.GC32719@linux.vnet.ibm.com> <5549DEAC.6080709@suse.cz> <20150508154726.9969933e6b5ebbb42e65ffae@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20150508154726.9969933e6b5ebbb42e65ffae@linux-foundation.org> Cc: Rik van Riel , anton@sambar.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko , Dave Hansen , Dan Streetman , Mel Gorman , Johannes Weiner , linuxppc-dev@lists.ozlabs.org, Vlastimil Babka List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 08.05.2015 [15:47:26 -0700], Andrew Morton wrote: > On Wed, 06 May 2015 11:28:12 +0200 Vlastimil Babka wrote: > > > On 05/06/2015 12:09 AM, Nishanth Aravamudan wrote: > > > On 03.04.2015 [10:45:56 -0700], Nishanth Aravamudan wrote: > > >>> What I find somewhat worrying though is that we could potentially > > >>> break the pfmemalloc_watermark_ok() test in situations where > > >>> zone_reclaimable_pages(zone) == 0 is a transient situation (and not > > >>> a permanently allocated hugepage). In that case, the throttling is > > >>> supposed to help system recover, and we might be breaking that > > >>> ability with this patch, no? > > >> > > >> Well, if it's transient, we'll skip it this time through, and once there > > >> are reclaimable pages, we should notice it again. > > >> > > >> I'm not familiar enough with this logic, so I'll read through the code > > >> again soon to see if your concern is valid, as best I can. > > > > > > In reviewing the code, I think that transiently unreclaimable zones will > > > lead to some higher direct reclaim rates and possible contention, but > > > shouldn't cause any major harm. The likelihood of that situation, as > > > well, in a non-reserved memory setup like the one I described, seems > > > exceedingly low. > > > > OK, I guess when a reasonably configured system has nothing to reclaim, > > it's already busted and throttling won't change much. > > > > Consider the patch Acked-by: Vlastimil Babka > > OK, thanks, I'll move this patch into the queue for 4.2-rc1. Thank you! > Or is it important enough to merge into 4.1? I think 4.2 is sufficient, but I wonder now if I should have included a stable tag? The issue has been around for a while and there's a relatively easily workaround (use the per-node sysfs files to manually round-robin around the exhausted node) in older kernels, so I had decided against it before. Thanks, Nish