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=-5.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 E79C0C35247 for ; Fri, 7 Feb 2020 03:36:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B85AB21927 for ; Fri, 7 Feb 2020 03:36:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="e2lTPZov" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727478AbgBGDgt (ORCPT ); Thu, 6 Feb 2020 22:36:49 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:43067 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726674AbgBGDgt (ORCPT ); Thu, 6 Feb 2020 22:36:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581046608; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kNfsZMrXvLDDzVoLhL2jmupSGehSTD9Rv6cnjwYywf4=; b=e2lTPZov5X9cx3mNVtEcy0XW4TdNuhcf5z/6/MlcDodEDU66xlqoNnpaKmpK4aQ/JR//Wd Ohpuq2Q5qO3mnsyd08R+4s7+gYCTES3l40Pk/qU0Ci+aCgQ9NHHsMyHnk+a26hM36V5CPU qeYotsiwiEn11WipYwJv+FwRAod1H8E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-60-6F2C0xAQMZucxI96X8Y58Q-1; Thu, 06 Feb 2020 22:36:44 -0500 X-MC-Unique: 6F2C0xAQMZucxI96X8Y58Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DA9A01088382; Fri, 7 Feb 2020 03:36:42 +0000 (UTC) Received: from localhost (ovpn-12-30.pek2.redhat.com [10.72.12.30]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 96643384; Fri, 7 Feb 2020 03:36:39 +0000 (UTC) Date: Fri, 7 Feb 2020 11:36:36 +0800 From: Baoquan He To: Dan Williams Cc: Wei Yang , Andrew Morton , Oscar Salvador , Linux MM , Linux Kernel Mailing List , David Hildenbrand Subject: Re: [PATCH 2/3] mm/sparsemem: get physical address to page struct instead of virtual address to pfn Message-ID: <20200207033636.GS8965@MiWiFi-R3L-srv> References: <20200206231629.14151-1-richardw.yang@linux.intel.com> <20200206231629.14151-3-richardw.yang@linux.intel.com> <20200207031011.GR8965@MiWiFi-R3L-srv> 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-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/20 at 07:21pm, Dan Williams wrote: > On Thu, Feb 6, 2020 at 7:10 PM Baoquan He wrote: > > > > Hi Dan, > > > > On 02/06/20 at 06:19pm, Dan Williams wrote: > > > On Thu, Feb 6, 2020 at 3:17 PM Wei Yang wrote: > > > > diff --git a/mm/sparse.c b/mm/sparse.c > > > > index b5da121bdd6e..56816f653588 100644 > > > > --- a/mm/sparse.c > > > > +++ b/mm/sparse.c > > > > @@ -888,7 +888,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn, > > > > /* Align memmap to section boundary in the subsection case */ > > > > if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) && > > > > section_nr_to_pfn(section_nr) != start_pfn) > > > > - memmap = pfn_to_kaddr(section_nr_to_pfn(section_nr)); > > > > + memmap = pfn_to_page(section_nr_to_pfn(section_nr)); > > > > > > Yes, this looks obviously correct. This might be tripping up > > > makedumpfile. Do you see any practical effects of this bug? The kernel > > > mostly avoids ->section_mem_map in the vmemmap case and in the > > > !vmemmap case section_nr_to_pfn(section_nr) should always equal > > > start_pfn. > > > > The practical effects is that the memmap for the first unaligned section will be lost > > when destroy namespace to hot remove it. Because we encode the ->section_mem_map > > into mem_section, and get memmap from the related mem_section to free it in > > section_deactivate(). In fact in vmemmap, we don't need to encode the ->section_mem_map > > with memmap. > > Right, but can you actually trigger that in the SPARSEMEM_VMEMMAP=n case? I think no, the lost memmap should only happen in vmemmap case. > > > By the way, sub-section support is only valid in vmemmap case, right? > > Yes. > > > Seems yes from code, but I don't find any document to prove it. > > check_pfn_span() enforces this requirement. Thanks for your confirmation. Do you mind if I add some document sentences somewhere make clear this?