From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751748AbdK3F6P (ORCPT ); Thu, 30 Nov 2017 00:58:15 -0500 Received: from mga06.intel.com ([134.134.136.31]:55758 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751488AbdK3F6L (ORCPT ); Thu, 30 Nov 2017 00:58:11 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.45,340,1508828400"; d="scan'208";a="7499074" Subject: Re: [PATCH 1/2] mm: NUMA stats code cleanup and enhancement To: Michal Hocko Cc: Greg Kroah-Hartman , Andrew Morton , Vlastimil Babka , Mel Gorman , Johannes Weiner , Christopher Lameter , YASUAKI ISHIMATSU , Andrey Ryabinin , Nikolay Borisov , Pavel Tatashin , David Rientjes , Sebastian Andrzej Siewior , Dave , Andi Kleen , Tim Chen , Jesper Dangaard Brouer , Ying Huang , Aaron Lu , Aubrey Li , Linux MM , Linux Kernel References: <1511848824-18709-1-git-send-email-kemi.wang@intel.com> <20171129121740.f6drkbktc43l5ib6@dhcp22.suse.cz> From: kemi Message-ID: <4b840074-cb5f-3c10-d65b-916bc02fb1ee@intel.com> Date: Thu, 30 Nov 2017 13:56:13 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171129121740.f6drkbktc43l5ib6@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年11月29日 20:17, Michal Hocko wrote: > On Tue 28-11-17 14:00:23, Kemi Wang wrote: >> The existed implementation of NUMA counters is per logical CPU along with >> zone->vm_numa_stat[] separated by zone, plus a global numa counter array >> vm_numa_stat[]. However, unlike the other vmstat counters, numa stats don't >> effect system's decision and are only read from /proc and /sys, it is a >> slow path operation and likely tolerate higher overhead. Additionally, >> usually nodes only have a single zone, except for node 0. And there isn't >> really any use where you need these hits counts separated by zone. >> >> Therefore, we can migrate the implementation of numa stats from per-zone to >> per-node, and get rid of these global numa counters. It's good enough to >> keep everything in a per cpu ptr of type u64, and sum them up when need, as >> suggested by Andi Kleen. That's helpful for code cleanup and enhancement >> (e.g. save more than 130+ lines code). > > I agree. Having these stats per zone is a bit of overcomplication. The > only consumer is /proc/zoneinfo and I would argue this doesn't justify > the additional complexity. Who does really need to know per zone broken > out numbers? > > Anyway, I haven't checked your implementation too deeply but why don't > you simply define static percpu array for each numa node? To be honest, there are another two ways I can think of listed below. but I don't think they are simpler than my current implementation. Maybe you have better idea. static u64 __percpu vm_stat_numa[num_possible_nodes() * NR_VM_NUMA_STAT_ITEMS]; But it's not correct. Or we can add an u64 percpu array with size of NR_VM_NUMA_STAT_ITEMS in struct pglist_data. My current implementation is quite straightforward by combining all of local counters together, only one percpu array with size of num_possible_nodes()*NR_VM_NUMA_STAT_ITEMS is enough for that. > [...] >> +extern u64 __percpu *vm_numa_stat; > [...] >> +#ifdef CONFIG_NUMA >> + size = sizeof(u64) * num_possible_nodes() * NR_VM_NUMA_STAT_ITEMS; >> + align = __alignof__(u64[num_possible_nodes() * NR_VM_NUMA_STAT_ITEMS]); >> + vm_numa_stat = (u64 __percpu *)__alloc_percpu(size, align); >> +#endif