From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56E00C433FF for ; Thu, 15 Aug 2019 08:46:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1495A2186A for ; Thu, 15 Aug 2019 08:46:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1495A2186A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B2E116B0010; Thu, 15 Aug 2019 04:46:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id ADE3E6B0266; Thu, 15 Aug 2019 04:46:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9F45A6B0269; Thu, 15 Aug 2019 04:46:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0100.hostedemail.com [216.40.44.100]) by kanga.kvack.org (Postfix) with ESMTP id 810146B0010 for ; Thu, 15 Aug 2019 04:46:36 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 2DF0552D5 for ; Thu, 15 Aug 2019 08:46:36 +0000 (UTC) X-FDA: 75824031192.11.bread45_73cceb08c4861 X-HE-Tag: bread45_73cceb08c4861 X-Filterd-Recvd-Size: 4886 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Thu, 15 Aug 2019 08:46:35 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 4F4BCAF0D; Thu, 15 Aug 2019 08:46:34 +0000 (UTC) Date: Thu, 15 Aug 2019 10:46:33 +0200 From: Michal Hocko To: Yang Shi Cc: kirill.shutemov@linux.intel.com, hannes@cmpxchg.org, vbabka@suse.cz, rientjes@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RESEND PATCH 1/2 -mm] mm: account lazy free pages separately Message-ID: <20190815084633.GF9477@dhcp22.suse.cz> References: <1565308665-24747-1-git-send-email-yang.shi@linux.alibaba.com> <20190809083216.GM18351@dhcp22.suse.cz> <1a3c4185-c7ab-8d6f-8191-77dce02025a7@linux.alibaba.com> <20190809180238.GS18351@dhcp22.suse.cz> <79c90f6b-fcac-02e1-015a-0eaa4eafdf7d@linux.alibaba.com> <20190812093430.GD5117@dhcp22.suse.cz> <297aefa2-ba64-cb91-d2c8-733054db01a3@linux.alibaba.com> <20190814110850.GT17933@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 14-08-19 21:51:47, Yang Shi wrote: > > > On 8/14/19 4:08 AM, Michal Hocko wrote: > > On Mon 12-08-19 10:00:17, Yang Shi wrote: > > > > > > On 8/12/19 2:34 AM, Michal Hocko wrote: > > > > On Fri 09-08-19 16:54:43, Yang Shi wrote: > > > > > On 8/9/19 11:26 AM, Yang Shi wrote: > > > > > > On 8/9/19 11:02 AM, Michal Hocko wrote: > > > > [...] > > > > > > > I have to study the code some more but is there any reason why those > > > > > > > pages are not accounted as proper THPs anymore? Sure they are partially > > > > > > > unmaped but they are still THPs so why cannot we keep them accounted > > > > > > > like that. Having a new counter to reflect that sounds like papering > > > > > > > over the problem to me. But as I've said I might be missing something > > > > > > > important here. > > > > > > I think we could keep those pages accounted for NR_ANON_THPS since they > > > > > > are still THP although they are unmapped as you mentioned if we just > > > > > > want to fix the improper accounting. > > > > > By double checking what NR_ANON_THPS really means, > > > > > Documentation/filesystems/proc.txt says "Non-file backed huge pages mapped > > > > > into userspace page tables". Then it makes some sense to dec NR_ANON_THPS > > > > > when removing rmap even though they are still THPs. > > > > > > > > > > I don't think we would like to change the definition, if so a new counter > > > > > may make more sense. > > > > Yes, changing NR_ANON_THPS semantic sounds like a bad idea. Let > > > > me try whether I understand the problem. So we have some THP in > > > > limbo waiting for them to be split and unmapped parts to be freed, > > > > right? I can see that page_remove_anon_compound_rmap does correctly > > > > decrement NR_ANON_MAPPED for sub pages that are no longer mapped by > > > > anybody. LRU pages seem to be accounted properly as well. As you've > > > > said NR_ANON_THPS reflects the number of THPs mapped and that should be > > > > reflecting the reality already IIUC. > > > > > > > > So the only problem seems to be that deferred THP might aggregate a lot > > > > of immediately freeable memory (if none of the subpages are mapped) and > > > > that can confuse MemAvailable because it doesn't know about the fact. > > > > Has an skewed counter resulted in a user observable behavior/failures? > > > No. But the skewed counter may make big difference for a big scale cluster. > > > The MemAvailable is an important factor for cluster scheduler to determine > > > the capacity. > > But MemAvailable is a very rough estimation. Is relying on it really a > > good measure? I mean there is a lot of reclaimable memory that is not > > reflected there (some fs. internal data structures, networking buffers > > etc.) > > Yes, I agree there are other freeable objects not accounted into > MemAvailable. Their size depends on the workload. But, deferred split THPs > seems more common with the common workloads. A simple run with MariaDB test > of mmtest shows it could generate over fifteen thousand deferred split THPs > (accumulated around 30G in one hour run, 75% of 40G memory for my VM). So, > it may be worth accounting deferred split THPs in MemAvailable. This is a very useful information to put into the changelog. -- Michal Hocko SUSE Labs