From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756754AbbJICf5 (ORCPT ); Thu, 8 Oct 2015 22:35:57 -0400 Received: from mga09.intel.com ([134.134.136.24]:50552 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752458AbbJICfz (ORCPT ); Thu, 8 Oct 2015 22:35:55 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.17,657,1437462000"; d="scan'208";a="660779104" Subject: Re: [Patch V3 2/9] kernel/profile.c: Replace cpu_to_mem() with cpu_to_node() To: David Rientjes 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> 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 From: Jiang Liu Organization: Intel Message-ID: <56172807.4090906@linux.intel.com> Date: Fri, 9 Oct 2015 10:35:51 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/8/20 8:00, David Rientjes wrote: > 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. Hi David, Sorry for slow response due to personal reasons! Function alloc_pages_exact_node() has been renamed as __alloc_pages_node() by commit 96db800f5d73, and __alloc_pages_node() is a slightly optimized version of alloc_pages_node() which doesn't fallback to current node for nid == NUMA_NO_NODE case. So it would be better to keep using __alloc_pages_node() because cpu_to_node() always returns valid node id. Thanks! Gerry > > 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/ >