Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751761AbbHTAA0 (ORCPT ); Wed, 19 Aug 2015 20:00:26 -0400 Received: from mail-pa0-f51.google.com ([209.85.220.51]:34946 "EHLO mail-pa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751344AbbHTAAY (ORCPT ); Wed, 19 Aug 2015 20:00:24 -0400 Date: Wed, 19 Aug 2015 17:00:22 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Jiang Liu cc: Andrew Morton , Mel Gorman , Mike Galbraith , Peter Zijlstra , "Rafael J . Wysocki" , Tang Chen , Tejun Heo , Tony Luck , linux-mm@kvack.org, linux-hotplug@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [Patch V3 2/9] kernel/profile.c: Replace cpu_to_mem() with cpu_to_node() In-Reply-To: <55D42DE3.2040506@linux.intel.com> Message-ID: References: <1439781546-7217-1-git-send-email-jiang.liu@linux.intel.com> <1439781546-7217-3-git-send-email-jiang.liu@linux.intel.com> <55D42DE3.2040506@linux.intel.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1644 Lines: 38 On Wed, 19 Aug 2015, Jiang Liu wrote: > On 2015/8/18 8:31, David Rientjes wrote: > > On Mon, 17 Aug 2015, Jiang Liu wrote: > > > >> Function profile_cpu_callback() allocates memory without specifying > >> __GFP_THISNODE flag, so replace cpu_to_mem() with cpu_to_node() > >> because cpu_to_mem() may cause suboptimal memory allocation if > >> there's no free memory on the node returned by cpu_to_mem(). > >> > > > > Why is cpu_to_node() better with regard to free memory and NUMA locality? > Hi David, > Thanks for review. This is a special case pointed out by Tejun. > For the imagined topology, A<->B<->X<->C<->D, where A, B, C, D has > memory and X is memoryless. > Possible fallback lists are: > B: [ B, A, C, D] > X: [ B, C, A, D] > C: [ C, D, B, A] > > cpu_to_mem(X) will either return B or C. Let's assume it returns B. > Then we will use "B: [ B, A, C, D]" to allocate memory for X, which > is not the optimal fallback list for X. And cpu_to_node(X) returns > X, and "X: [ B, C, A, D]" is the optimal fallback list for X. Ok, that makes sense, but I would prefer that this alloc_pages_exact_node() change to alloc_pages_node() since, as you mention in your commit message, __GFP_THISNODE is not set. In the longterm, if we setup both zonelists correctly (no __GFP_THISNODE and with __GFP_THISNODE), then I'm not sure there's any reason to ever use cpu_to_mem() for alloc_pages(). -- 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/