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,UNPARSEABLE_RELAY autolearn=unavailable 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 1C0EBC46470 for ; Tue, 14 May 2019 20:44:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E9D0320850 for ; Tue, 14 May 2019 20:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726569AbfENUoo (ORCPT ); Tue, 14 May 2019 16:44:44 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:44809 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726265AbfENUoo (ORCPT ); Tue, 14 May 2019 16:44:44 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0TRkUBgw_1557866676; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TRkUBgw_1557866676) by smtp.aliyun-inc.com(127.0.0.1); Wed, 15 May 2019 04:44:40 +0800 Subject: Re: [v2 PATCH] mm: vmscan: correct nr_reclaimed for THP To: Michal Hocko , Yang Shi Cc: Huang Ying , Johannes Weiner , Mel Gorman , kirill.shutemov@linux.intel.com, Hugh Dickins , Shakeel Butt , william.kucharski@oracle.com, Andrew Morton , Linux MM , Linux Kernel Mailing List References: <1557505420-21809-1-git-send-email-yang.shi@linux.alibaba.com> <20190513080929.GC24036@dhcp22.suse.cz> <20190513214503.GB25356@dhcp22.suse.cz> <20190514062039.GB20868@dhcp22.suse.cz> From: Yang Shi Message-ID: <509de066-17bb-e3cf-d492-1daf1cb11494@linux.alibaba.com> Date: Tue, 14 May 2019 13:44:35 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20190514062039.GB20868@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/13/19 11:20 PM, Michal Hocko wrote: > On Mon 13-05-19 21:36:59, Yang Shi wrote: >> On Mon, May 13, 2019 at 2:45 PM Michal Hocko wrote: >>> On Mon 13-05-19 14:09:59, Yang Shi wrote: >>> [...] >>>> I think we can just account 512 base pages for nr_scanned for >>>> isolate_lru_pages() to make the counters sane since PGSCAN_KSWAPD/DIRECT >>>> just use it. >>>> >>>> And, sc->nr_scanned should be accounted as 512 base pages too otherwise we >>>> may have nr_scanned < nr_to_reclaim all the time to result in false-negative >>>> for priority raise and something else wrong (e.g. wrong vmpressure). >>> Be careful. nr_scanned is used as a pressure indicator to slab shrinking >>> AFAIR. Maybe this is ok but it really begs for much more explaining >> I don't know why my company mailbox didn't receive this email, so I >> replied with my personal email. >> >> It is not used to double slab pressure any more since commit >> 9092c71bb724 ("mm: use sc->priority for slab shrink targets"). It uses >> sc->priority to determine the pressure for slab shrinking now. >> >> So, I think we can just remove that "double slab pressure" code. It is >> not used actually and looks confusing now. Actually, the "double slab >> pressure" does something opposite. The extra inc to sc->nr_scanned >> just prevents from raising sc->priority. > I have to get in sync with the recent changes. I am aware there were > some patches floating around but I didn't get to review them. I was > trying to point out that nr_scanned used to have a side effect to be > careful about. If it doesn't have anymore then this is getting much more > easier of course. Please document everything in the changelog. Thanks for reminding. Yes, I remembered nr_scanned would double slab pressure. But, when I inspected into the code yesterday, it turns out it is not true anymore. I will run some test to make sure it doesn't introduce regression. BTW, I noticed the counter of memory reclaim is not correct with THP swap on vanilla kernel, please see the below: pgsteal_kswapd 21435 pgsteal_direct 26573329 pgscan_kswapd 3514 pgscan_direct 14417775 pgsteal is always greater than pgscan, my patch could fix the problem. Anyway, I will elaborate these in the commit log.