From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 7768F6B0038 for ; Sun, 17 Sep 2017 22:46:12 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id f84so13564501pfj.0 for ; Sun, 17 Sep 2017 19:46:12 -0700 (PDT) Received: from mga05.intel.com (mga05.intel.com. [192.55.52.43]) by mx.google.com with ESMTPS id 12si4309143plb.264.2017.09.17.19.46.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 17 Sep 2017 19:46:11 -0700 (PDT) Subject: Re: [PATCH 1/3] mm, sysctl: make VM stats configurable References: <1505467406-9945-1-git-send-email-kemi.wang@intel.com> <1505467406-9945-2-git-send-email-kemi.wang@intel.com> <20170915114952.czb7nbsioqguxxk3@dhcp22.suse.cz> <20170915142823.jlhsba6rdhx5glfe@dhcp22.suse.cz> From: kemi Message-ID: Date: Mon, 18 Sep 2017 10:44:52 +0800 MIME-Version: 1.0 In-Reply-To: <20170915142823.jlhsba6rdhx5glfe@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Dave Hansen Cc: "Luis R . Rodriguez" , Kees Cook , Andrew Morton , Jonathan Corbet , Mel Gorman , Johannes Weiner , Christopher Lameter , Sebastian Andrzej Siewior , Vlastimil Babka , Hillf Danton , Tim Chen , Andi Kleen , Jesper Dangaard Brouer , Ying Huang , Aaron Lu , Proc sysctl , Linux MM , Linux Kernel On 2017a1'09ae??15ae?JPY 22:28, Michal Hocko wrote: > On Fri 15-09-17 07:16:23, Dave Hansen wrote: >> On 09/15/2017 04:49 AM, Michal Hocko wrote: >>> Why do we need an auto-mode? Is it safe to enforce by default. >> >> Do we *need* it? Not really. >> >> But, it does offer the best of both worlds: The vast majority of users >> see virtually no impact from the counters. The minority that do need >> them pay the cost *and* don't have to change their tooling at all. > > Just to make it clear, I am not really opposing. It just adds some code > which we can safe... It is also rather chatty for something that can be > true/false. > It has benefit, as Dave mentioned above. Actually, it adds some coding complexity to provide a tuning interface with on/off/auto mode. Using human-readable string instead of magic number makes it easier to use, people probably don't need to review the ABI doc again before using it. So, I don't think that should be a problem >>> Is it> possible that userspace can get confused to see 0 NUMA stats in >> the >>> first read while other allocation stats are non-zero? >> >> I doubt it. Those counters are pretty worthless by themselves. I have >> tooling that goes and reads them, but it aways displays deltas. Read >> stats, sleep one second, read again, print the difference. > > This is how I use them as well. > >> The only scenario I can see mattering is someone who is seeing a >> performance issue due to NUMA allocation misses (or whatever) and wants >> to go look *back* in the past. > > yes > If it really matters, setting vmstat_mode=strict as a default option is a simple way to fix it. What's your idea? thanks >> A single-time printk could also go a long way to keeping folks from >> getting confused. > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org