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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 C9E97C43444 for ; Thu, 10 Jan 2019 09:46:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4F70214DA for ; Thu, 10 Jan 2019 09:46:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727959AbfAJJqK (ORCPT ); Thu, 10 Jan 2019 04:46:10 -0500 Received: from relay.sw.ru ([185.231.240.75]:55640 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727863AbfAJJqK (ORCPT ); Thu, 10 Jan 2019 04:46:10 -0500 Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1ghWua-0003EX-Uo; Thu, 10 Jan 2019 12:46:05 +0300 Subject: Re: [PATCH RFC 0/3] mm: Reduce IO by improving algorithm of memcg pagecache pages eviction To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , josef@toxicpanda.com, Jan Kara , Hugh Dickins , "Darrick J. Wong" , Michal Hocko , Andrey Ryabinin , Roman Gushchin , Mel Gorman , Linux MM , LKML References: <154703479840.32690.6504699919905946726.stgit@localhost.localdomain> From: Kirill Tkhai Message-ID: Date: Thu, 10 Jan 2019 12:46:04 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Shakeel, On 09.01.2019 20:37, Shakeel Butt wrote: > Hi Kirill, > > On Wed, Jan 9, 2019 at 4:20 AM Kirill Tkhai wrote: >> >> On nodes without memory overcommit, it's common a situation, >> when memcg exceeds its limit and pages from pagecache are >> shrinked on reclaim, while node has a lot of free memory. >> Further access to the pages requires real device IO, while >> IO causes time delays, worse powerusage, worse throughput >> for other users of the device, etc. >> >> Cleancache is not a good solution for this problem, since >> it implies copying of page on every cleancache_put_page() >> and cleancache_get_page(). Also, it requires introduction >> of internal per-cleancache_ops data structures to manage >> cached pages and their inodes relationships, which again >> introduces overhead. >> >> This patchset introduces another solution. It introduces >> a new scheme for evicting memcg pages: >> >> 1)__remove_mapping() uncharges unmapped page memcg >> and leaves page in pagecache on memcg reclaim; >> >> 2)putback_lru_page() places page into root_mem_cgroup >> list, since its memcg is NULL. Page may be evicted >> on global reclaim (and this will be easily, as >> page is not mapped, so shrinker will shrink it >> with 100% probability of success); >> >> 3)pagecache_get_page() charges page into memcg of >> a task, which takes it first. >> > > From what I understand from the proposal, on memcg reclaim, the file > pages are uncharged but kept in the memory and if they are accessed > again (either through mmap or syscall), they will be charged again but > to the requesting memcg. Also it is assumed that the global reclaim of > such uncharged file pages is very fast and deterministic. Is that > right? Yes, this was my assumption. But Michal, Josef and Johannes pointed a diving into reclaim in general is not fast. So, maybe we need some more creativity here to minimize the effect of this diving.. Thanks, Kirill