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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 102B2C33CB1 for ; Fri, 17 Jan 2020 07:14:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9B2A02073A for ; Fri, 17 Jan 2020 07:14:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="PtdK7itT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9B2A02073A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 03BA16B0323; Fri, 17 Jan 2020 02:14:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id F2ECE6B0324; Fri, 17 Jan 2020 02:14:16 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E44BC6B0325; Fri, 17 Jan 2020 02:14:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0057.hostedemail.com [216.40.44.57]) by kanga.kvack.org (Postfix) with ESMTP id CDF286B0323 for ; Fri, 17 Jan 2020 02:14:16 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 93FDF180AD815 for ; Fri, 17 Jan 2020 07:14:16 +0000 (UTC) X-FDA: 76386262512.04.lake66_251e6cd979129 X-HE-Tag: lake66_251e6cd979129 X-Filterd-Recvd-Size: 3969 Received: from mail-oi1-f193.google.com (mail-oi1-f193.google.com [209.85.167.193]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Fri, 17 Jan 2020 07:14:14 +0000 (UTC) Received: by mail-oi1-f193.google.com with SMTP id l136so21340425oig.1 for ; Thu, 16 Jan 2020 23:14:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=7Eh95S1MlzTY8i0LF9De8ZEjwbrXfDSgRBgCgMZN1jc=; b=PtdK7itThPrlobYA0Dg2bXwzk5LU9ZuTVVxf8p129PJdHS/bL6lppGsoulmvj4PW+u U7lB5oEEvp43/osZ4EUr7/GwRFdvzxlVPEsw6Ww+iqgx7vEgpiASbAAqTR8K1UJQqnvS KJ1zjVijBAnIIWMqFCudydgUWvEYu42RFRO+xD1OLnQi/8IhTYx5XHwto8kir+4L4ubc +8gQQz9CluoBDQh/bvfLWvXWSHGwqHTMVovCT1LLSSoe5wQjQuhkED+mJUYNuJ3icdFr glAjHnA2FfhSY1thq9lldApViWPBqUOTBdOS+fkrB4dJDXH/J/CNciOmqLUB2zVM1byO upYw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7Eh95S1MlzTY8i0LF9De8ZEjwbrXfDSgRBgCgMZN1jc=; b=b0p6Ksqevey1ujQ6bu/UsA6PN3/pikY3pqE5Cir+b1KjXD8emlXWKyfni48AmjlT5f bITbP4z2HNmZeXsUX6rMoMzlhZeLOmgiwL+BCicNJ+qW4ZbnLbzgG+/+1j3/MI1rfYEh ngqsirHgLyDVaLC0d5SrPb5FCgQHoEziLIMcQRQzamRQV+qZPJvguhlQKpgjI6x4gET+ D5bXs9U1bi9ZI0nzDEKjYfyrrl9QsIbB7IsJV8jbbxdsLBOHy6MgSP0ykCoAuowQFA+A D4hFPtkp/ocq/jZCbb2BzmnG1fqJSvZr7v/2FdnVpSl6GNb4jIuVSfHQqHvZmrKr07gm upoA== X-Gm-Message-State: APjAAAUx0o9jagALKW6lsg6bhzz/TewkZ+cMX6VNHQLKRRtg+6+4fsfT YZqJTsaQtrBsEby6EFmc7aompdgdcldwIhVv7hf44Y6T X-Google-Smtp-Source: APXvYqypKTw4sEA4efwNVMpM3vKeTNYiY2iTt/kIwA5yao8p911aPKCxKbPynaSkrtbhAJ3DBWjUon9irr6kTISakhU= X-Received: by 2002:aca:1103:: with SMTP id 3mr2324674oir.70.1579245253453; Thu, 16 Jan 2020 23:14:13 -0800 (PST) MIME-Version: 1.0 References: <1579143668-27941-1-git-send-email-kernelfans@gmail.com> <20200116075000.GM19428@dhcp22.suse.cz> In-Reply-To: From: Dan Williams Date: Thu, 16 Jan 2020 23:14:02 -0800 Message-ID: Subject: Re: [PATCH] mm/sparse: reset section's mem_map when fully deactivated To: Pingfan Liu Cc: Michal Hocko , Linux-MM , Andrew Morton , David Hildenbrand , Oscar Salvador , Kexec Mailing List , Kazuhito Hagio Content-Type: text/plain; charset="UTF-8" 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 Thu, Jan 16, 2020 at 10:23 PM Pingfan Liu wrote: > > On Thu, Jan 16, 2020 at 3:50 PM Michal Hocko wrote: > > > > On Thu 16-01-20 11:01:08, Pingfan Liu wrote: > > > When fully deactivated, it is meaningless to keep the value of a section's > > > mem_map. And its mem_map will be reassigned during re-added. > > > > > > Beside this, it breaks the user space tool "makedumpfile", which makes > > > assumption that a hot-removed section having mem_map as NULL. > > > > We used to do that before ba72b4c8cf60 ("mm/sparsemem: support > > sub-section hotplug"). Dan was this an intentional change? > I do not know the purpose of this. But the change just leave section > start pfn in fully deactivated section_mem_map, and not used any more. Not intentional, IIRC at the time I had convinced myself that the value would always be translated by sparse_decode_mem_map(), so I thought it could be hiding NULL de-references. I don't see any harm in the patch.