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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 C8009C43387 for ; Mon, 17 Dec 2018 09:35:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 909EB206A2 for ; Mon, 17 Dec 2018 09:35:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732048AbeLQJfH (ORCPT ); Mon, 17 Dec 2018 04:35:07 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34194 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726622AbeLQJfG (ORCPT ); Mon, 17 Dec 2018 04:35:06 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EF83A8DA5B; Mon, 17 Dec 2018 09:35:04 +0000 (UTC) Received: from [10.36.117.250] (ovpn-117-250.ams2.redhat.com [10.36.117.250]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1EB7B60F8D; Mon, 17 Dec 2018 09:34:59 +0000 (UTC) Subject: Re: [PATCH v1 9/9] mm: better document PG_reserved To: Randy Dunlap , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-m68k@lists.linux-m68k.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-mediatek@lists.infradead.org, Andrew Morton , Stephen Rothwell , Pavel Tatashin , Michal Hocko , Alexander Duyck , Matthew Wilcox , Anthony Yznaga , Miles Chen , yi.z.zhang@linux.intel.com, Dan Williams References: <20181214111014.15672-1-david@redhat.com> <20181214111014.15672-10-david@redhat.com> <03f65c6f-1287-4c63-6705-16e58d659d94@infradead.org> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: Date: Mon, 17 Dec 2018 10:34:59 +0100 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: <03f65c6f-1287-4c63-6705-16e58d659d94@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Mon, 17 Dec 2018 09:35:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15.12.18 01:12, Randy Dunlap wrote: > On 12/14/18 3:10 AM, David Hildenbrand wrote: >> The usage of PG_reserved and how PG_reserved pages are to be treated is >> buried deep down in different parts of the kernel. Let's shine some light >> onto these details by documenting current users and expected >> behavior. >> >> Especially, clarify on the "Some of them might not even exist" case. >> These are physical memory gaps that will never be dumped as they >> are not marked as IORESOURCE_SYSRAM. PG_reserved does in general not >> hinder anybody from dumping or swapping. In some cases, these pages >> will not be stored in the hibernation image. > > Hi, > Thanks for the doc update. > Comments below. > >> Cc: Andrew Morton >> Cc: Stephen Rothwell >> Cc: Pavel Tatashin >> Cc: Michal Hocko >> Cc: Alexander Duyck >> Cc: Matthew Wilcox >> Cc: Anthony Yznaga >> Cc: Miles Chen >> Cc: yi.z.zhang@linux.intel.com >> Cc: Dan Williams >> Signed-off-by: David Hildenbrand >> --- >> include/linux/page-flags.h | 33 +++++++++++++++++++++++++++++++-- >> 1 file changed, 31 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index 808b4183e30d..9de2e941cbd5 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h >> @@ -17,8 +17,37 @@ >> /* >> * Various page->flags bits: >> * >> - * PG_reserved is set for special pages, which can never be swapped out. Some >> - * of them might not even exist... >> + * PG_reserved is set for special pages. The "struct page" of such a page >> + * should in general not be touched (e.g. set dirty) except by their owner. > > by its owner. Indeed. > >> + * Pages marked as PG_reserved include: >> + * - Pages part of the kernel image (including vDSO) and similar (e.g. BIOS, >> + * initrd, HW tables) >> + * - Pages reserved or allocated early during boot (before the page allocator >> + * was initialized). This includes (depending on the architecture) the >> + * initial vmmap, initial page tables, crashkernel, elfcorehdr, and much > > VM map, This should actually be vmemmap (aka struct pages). > >> + * much more. Once (if ever) freed, PG_reserved is cleared and they will >> + * be given to the page allocator. >> + * - Pages falling into physical memory gaps - not IORESOURCE_SYSRAM. Trying >> + * to read/write these pages might end badly. Don't touch! >> + * - The zero page(s) >> + * - Pages not added to the page allocator when onlining a section because >> + * they were excluded via the online_page_callback() or because they are >> + * PG_hwpoison. >> + * - Pages allocated in the context of kexec/kdump (loaded kernel image, >> + * control pages, vmcoreinfo) >> + * - MMIO/DMA pages. Some architectures don't allow to ioremap pages that are >> + * not marked PG_reserved (as they might be in use by somebody else who does >> + * not respect the caching strategy). >> + * - Pages part of an offline section (struct pages of offline sections should >> + * not be trusted as they will be initialized when first onlined). >> + * - MCA pages on ia64 >> + * - Pages holding CPU notes for POWER Firmware Assisted Dump >> + * - Device memory (e.g. PMEM, DAX, HMM) >> + * Some PG_reserved pages will be excluded from the hibernation image. >> + * PG_reserved does in general not hinder anybody from dumping or swapping >> + * and is no longer required for remap_pfn_range(). ioremap might require it. >> + * Consequently, PG_reserved for a page mapped into user space can indicate >> + * the zero page, the vDSO, MMIO pages or device memory. >> * >> * The PG_private bitflag is set on pagecache pages if they contain filesystem >> * specific data (which is normally at page->private). It can be used by >> > > cheers. > Thanks! -- Thanks, David / dhildenb