Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932570AbbD0LCe (ORCPT ); Mon, 27 Apr 2015 07:02:34 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:9732 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752490AbbD0LCc (ORCPT ); Mon, 27 Apr 2015 07:02:32 -0400 X-IronPort-AV: E=Sophos;i="5.04,848,1406563200"; d="scan'208";a="91288880" Message-ID: <553E0D44.9030104@cn.fujitsu.com> Date: Mon, 27 Apr 2015 18:19:48 +0800 From: Gu Zheng User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:7.0.1) Gecko/20110930 Thunderbird/7.0.1 MIME-Version: 1.0 To: Andrew Morton CC: , , , , , , , , , , , Subject: Re: [RESEND RFC PATCH 2/2] gfp: use the best near online node if the target node is offline References: <1429869513-2906-1-git-send-email-guz.fnst@cn.fujitsu.com> <1429869513-2906-2-git-send-email-guz.fnst@cn.fujitsu.com> <20150424130153.f7b494f1533529651b2696c6@linux-foundation.org> In-Reply-To: <20150424130153.f7b494f1533529651b2696c6@linux-foundation.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.100] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3087 Lines: 100 Hi Andrew, On 04/25/2015 04:01 AM, Andrew Morton wrote: > On Fri, 24 Apr 2015 17:58:33 +0800 Gu Zheng wrote: > >> Since the change to the cpu <--> mapping (map the cpu to the physical >> node for all possible at the boot), the node of cpu may be not present, >> so we use the best near online node if the node is not present in the low >> level allocation APIs. >> >> ... >> >> --- a/include/linux/gfp.h >> +++ b/include/linux/gfp.h >> @@ -298,9 +298,31 @@ __alloc_pages(gfp_t gfp_mask, unsigned int order, >> return __alloc_pages_nodemask(gfp_mask, order, zonelist, NULL); >> } >> >> +static int find_near_online_node(int node) >> +{ >> + int n, val; >> + int min_val = INT_MAX; >> + int best_node = -1; >> + >> + for_each_online_node(n) { >> + val = node_distance(node, n); >> + >> + if (val < min_val) { >> + min_val = val; >> + best_node = n; >> + } >> + } >> + >> + return best_node; >> +} > > This should be `inline' if it's in a header file. > > But it is far too large to be inlined anyway - please move it to a .c file. Agree. > > And please document it. A critical thing to describe is how we > determine whether a node is "near". There are presumably multiple ways > in which we could decide that a node is "near" (number of hops, minimum > latency, ...). Which one did you choose, and why? It just reuse the dropped code in PATCH 1/2, based on the node_distance table, which is a arch special defined one, and the data mostly comes from the firmware info, e.g. SLIT table. > >> static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask, >> unsigned int order) >> { >> + /* Offline node, use the best near online node */ >> + if (!node_online(nid)) >> + nid = find_near_online_node(nid); >> + >> /* Unknown node is current node */ >> if (nid < 0) >> nid = numa_node_id(); >> @@ -311,7 +333,11 @@ static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask, >> static inline struct page *alloc_pages_exact_node(int nid, gfp_t gfp_mask, >> unsigned int order) >> { >> - VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES || !node_online(nid)); >> + /* Offline node, use the best near online node */ >> + if (!node_online(nid)) >> + nid = find_near_online_node(nid); >> + >> + VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); >> >> return __alloc_pages(gfp_mask, order, node_zonelist(nid, gfp_mask)); >> } > > Ouch. These functions are called very frequently, and adding overhead > to them is a big deal. And the patch even adds overhead to non-x86 > architectures which don't benefit from it! > > Is there no way this problem can be fixed somewhere else? Preferably > by fixing things up at hotplug time. As Kame suggested, maintaining a per-cpu cache about the alternative-node only for x86 arch seems a good choice. Regards, Gu > . > -- 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/