Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932660AbbD0LCk (ORCPT ); Mon, 27 Apr 2015 07:02:40 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:20148 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752622AbbD0LCd (ORCPT ); Mon, 27 Apr 2015 07:02:33 -0400 X-IronPort-AV: E=Sophos;i="5.04,848,1406563200"; d="scan'208";a="91288881" Message-ID: <553E0ED8.8040209@cn.fujitsu.com> Date: Mon, 27 Apr 2015 18:26:32 +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: Kamezawa Hiroyuki CC: Andrew Morton , , , , , , , , , , , 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> <553E0510.9040001@jp.fujitsu.com> In-Reply-To: <553E0510.9040001@jp.fujitsu.com> Content-Type: text/plain; charset="windows-1252" 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: 3301 Lines: 107 Hi Kame-san, On 04/27/2015 05:44 PM, Kamezawa Hiroyuki wrote: > On 2015/04/25 5:01, 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. >> >> 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? >> >>> 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); > > In above VM_BUG_ON(), !node_online(nid) is the bug. But it will be possible here with the change in PATCH 1/2. > >>> + >>> + 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. > > I agree. the results should be cached. If necessary, in per-cpu line. Sounds great, will try this way. Regards, Gu > > > Thanks, > -Kame > > > . > -- 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/