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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 07B30C2BB55 for ; Thu, 16 Apr 2020 19:03:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AD42121973 for ; Thu, 16 Apr 2020 19:02:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AD42121973 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 1001F8E00DF; Thu, 16 Apr 2020 15:02:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0B1448E00BC; 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16 Apr 2020 12:02:55 -0700 IronPort-SDR: ymq36zYJgR/7G957GC04BbdJKU/RbEgRmUIlu1MMdl3U0v53ei+MWGiscHTnQ+dQAQVTRa3O0F jWEw3kqZdaIg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,392,1580803200"; d="scan'208";a="257325450" Received: from cchyder-mobl1.amr.corp.intel.com (HELO [10.254.70.41]) ([10.254.70.41]) by orsmga006.jf.intel.com with ESMTP; 16 Apr 2020 12:02:54 -0700 Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages To: Claudio Imbrenda Cc: Peter Zijlstra , Andy Lutomirski , linux-next@vger.kernel.org, akpm@linux-foundation.org, jack@suse.cz, kirill@shutemov.name, "Edgecombe, Rick P" , Sean Christopherson , borntraeger@de.ibm.com, david@redhat.com, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Will Deacon , "Williams, Dan J" References: <20200306132537.783769-1-imbrenda@linux.ibm.com> <20200306132537.783769-3-imbrenda@linux.ibm.com> <3ae46945-0c7b-03cd-700a-a6fe8003c6ab@intel.com> <20200415221754.GM2483@worktop.programming.kicks-ass.net> <20200416141547.29be5ea0@p-imbrenda> <20200416165900.68bd4dba@p-imbrenda> <20200416183431.7216e1d1@p-imbrenda> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20200416183431.7216e1d1@p-imbrenda> Content-Type: text/plain; charset=utf-8 Content-Language: en-US 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: On 4/16/20 9:34 AM, Claudio Imbrenda wrote: >> Ahh, so this is *just* intended to precede I/O done on the page, when >> a non-host entity is touching the memory? > yep OK, so we've got to do an action that precedes *all* I/O to a page. That's not too bad. I still don't understand how this could work generally, though There are lots of places where I/O is done to a page without either going through __test_set_page_writeback() or gup() with FOLL_PIN set. sendfile() is probably the best example of this: fd =3D open("/normal/ext4/file", O_RDONLY); sendfile(socket_fd, fd, &off, count); There's no gup in sight since the file doesn't have an address and it's not being written to so there's no writeback. How does sendfile work?