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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 50DE6C433DF for ; Wed, 24 Jun 2020 22:05:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1837020768 for ; Wed, 24 Jun 2020 22:05:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389016AbgFXWF5 (ORCPT ); Wed, 24 Jun 2020 18:05:57 -0400 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:59471 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388778AbgFXWF4 (ORCPT ); Wed, 24 Jun 2020 18:05:56 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R821e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0U0d59pt_1593036352; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U0d59pt_1593036352) by smtp.aliyun-inc.com(127.0.0.1); Thu, 25 Jun 2020 06:05:52 +0800 Date: Thu, 25 Jun 2020 06:05:52 +0800 From: Wei Yang To: Dan Williams Cc: Wei Yang , Michal Hocko , Andrew Morton , Oscar Salvador , Linux MM , Baoquan He , Linux Kernel Mailing List , David Hildenbrand Subject: Re: [PATCH] mm/spase: never partially remove memmap for early section Message-ID: <20200624220552.GA15016@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200623094258.6705-1-richard.weiyang@linux.alibaba.com> <20200623151828.GA31426@dhcp22.suse.cz> <20200624061340.GA11552@L-31X9LVDL-1304.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 24, 2020 at 09:10:09AM -0700, Dan Williams wrote: >On Tue, Jun 23, 2020 at 11:14 PM Wei Yang > wrote: >> >> On Tue, Jun 23, 2020 at 05:18:28PM +0200, Michal Hocko wrote: >> >On Tue 23-06-20 17:42:58, Wei Yang wrote: >> >> For early sections, we assumes its memmap will never be partially >> >> removed. But current behavior breaks this. >> >> >> >> Let's correct it. >> >> >> >> Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") >> >> Signed-off-by: Wei Yang >> > >> >Can a user trigger this or is this a theoretical bug? >> >> Let me rewrite the changelog a little. Look forward any comments. >> >> For early sections, its memmap is handled specially even sub-section is >> enabled. The memmap could only be populated as a whole. >> >> Quoted from the comment of section_activate(): >> >> * The early init code does not consider partially populated >> * initial sections, it simply assumes that memory will never be >> * referenced. If we hot-add memory into such a section then we >> * do not need to populate the memmap and can simply reuse what >> * is already there. >> >> While current section_deactivate() breaks this rule. When hot-remove a >> sub-section, section_deactivate() would depopulate its memmap. The >> consequence is if we hot-add this subsection again, its memmap never get >> proper populated. > >Ok, forgive the latency as re-fetched this logic into my mental cache. >So what I was remembering was the initial state of the code that >special cased early sections, and that still seems to be the case in >pfn_valid(). IIRC early_sections / bootmem are blocked from being >removed entirely. Partial / subsection removals are ok. Would you mind giving more words? Partial subsection removal is ok, so no need to fix this? -- Wei Yang Help you, Help me