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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 32E27C433DB for ; Thu, 18 Feb 2021 11:38:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AEB4C60C41 for ; Thu, 18 Feb 2021 11:38:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AEB4C60C41 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2B0766B006E; Thu, 18 Feb 2021 06:38:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 260076B0070; Thu, 18 Feb 2021 06:38:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 14ECA6B0071; Thu, 18 Feb 2021 06:38:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0141.hostedemail.com [216.40.44.141]) by kanga.kvack.org (Postfix) with ESMTP id F34DD6B006E for ; Thu, 18 Feb 2021 06:38:47 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id B9D414DD0 for ; Thu, 18 Feb 2021 11:38:47 +0000 (UTC) X-FDA: 77831191494.20.bomb89_1f025d327654 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id 9A9BD180C07A3 for ; Thu, 18 Feb 2021 11:38:47 +0000 (UTC) X-HE-Tag: bomb89_1f025d327654 X-Filterd-Recvd-Size: 6356 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by imf32.hostedemail.com (Postfix) with ESMTP for ; Thu, 18 Feb 2021 11:38:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613648326; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3A4zaSGP/jDU0jQya7nJb+PtO132rNXYV3X5vurWHRM=; b=FsnxXWc2e03gNM9vf6/ZY/Yo7E9exlCDot+KyryDAdQ2JH3jarJj+EpjyHE1+DvUCQVup8 ruVnGUhFmzEx1y/JrlRJ9ko6K/iUOsnq5hh/NMrucNOPrVVyjvSihc7lQZVxqot01/fVmd 8hLWbHxsl5xzjkam9TZ7EQaVOA5WyIk= 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-280-fC5elPu5OAqWLO01C1hoPg-1; Thu, 18 Feb 2021 06:38:42 -0500 X-MC-Unique: fC5elPu5OAqWLO01C1hoPg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0A5F3801965; Thu, 18 Feb 2021 11:38:39 +0000 (UTC) Received: from [10.36.114.59] (ovpn-114-59.ams2.redhat.com [10.36.114.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id B12B16F7EC; Thu, 18 Feb 2021 11:38:28 +0000 (UTC) To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Arnd Bergmann , Oscar Salvador , Matthew Wilcox , Andrea Arcangeli , Minchan Kim , Jann Horn , Jason Gunthorpe , Dave Hansen , Hugh Dickins , Rik van Riel , "Michael S . Tsirkin" , "Kirill A . Shutemov" , Vlastimil Babka , Richard Henderson , Ivan Kokshaysky , Matt Turner , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Chris Zankel , Max Filippov , linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org References: <20210217154844.12392-1-david@redhat.com> <3763a505-02d6-5efe-a9f5-40381acfbdfd@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH RFC] mm/madvise: introduce MADV_POPULATE to prefault/prealloc memory Message-ID: <740cdd51-137b-2b08-8b7f-9757d8d847cb@redhat.com> Date: Thu, 18 Feb 2021 12:38:27 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Content-Transfer-Encoding: quoted-printable 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: >>>> If we hit >>>> hardware errors on pages, ignore them - nothing we really can o= r >>>> should do. >>>> 3. On errors during MADV_POPULATED, some memory might have been >>>> populated. Callers have to clean up if they care. >>> >>> How does caller find out? madvise reports 0 on success so how do you >>> find out how much has been populated? >> >> If there is an error, something might have been populated. In my QEMU >> implementation, I simply discard the range again, good enough. I don't= think >> we need to really indicate "error and populated" or "error and not >> populated". >=20 > Agreed. The wording just suggests that the syscall actually provides an= y > means for an effective way to handle those errors. Maybe you should jus= t > stick with the first sentence and drop the second. Makes sense. "On errors during MADV_POPULATE, some memory might have=20 been populated." > =20 >>>> 4. Concurrent changes to the virtual memory layour are tolerated - w= e >>>> process each and every PFN only once, though. >>> >>> I do not understand this. madvise is about virtual address space not = a >>> physical address space. >> >> What I wanted to express: if we detect a change in the mapping we don'= t >> restart at the beginning, we always make forward progress. We process = each >> virtual address once (on a per-page basis, thus I accidentally used "P= FN"). >=20 > This is an implicit assumption. Your range can have the same page mappe= d > several times in the given address range and all you care about is that > you fault those which are not present during the virtual address space > walk. Your syscall can return and large part of the address space might > be unpopulated because memory reclaim just dropped those pages and that > would be fine. This shouldn't really imply memory presence - mlock does > that. "Concurrent changes to the virtual memory layout are tolerated. The=20 range is processed exactly once." >=20 >>>> 5. If MADV_POPULATE succeeds, all memory in the range can be accesse= d >>>> without SIGBUS. (of course, not if user space changed mappings = in the >>>> meantime or KSM kicked in on anonymous memory). >>> >>> I do not see how KSM would change anything here and maybe it is not >>> really important to mention it. KSM should be really transparent from >>> the users space POV. Parallel and destructive virtual address space >>> operations are also expected to change the outcome and there is nothi= ng >>> kernel do about at and provide any meaningful guarantees. I guess we >>> want to assume a reasonable userspace behavior here. >> >> It's just a note that we cannot protect from someone interfering >> (discard/ksm/whatever). I'm making that clearer in the cover letter. >=20 > Again that is implicit expectation. madvise will not work for anybody > shooting an own foot. Okay, I'll drop that part, thanks! --=20 Thanks, David / dhildenb