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=-2.3 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 90BA8C55185 for ; Tue, 21 Apr 2020 21:31:33 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2CE85206E9 for ; Tue, 21 Apr 2020 21:31:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CE85206E9 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 801D88E0005; Tue, 21 Apr 2020 17:31:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7B3418E0003; 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21 Apr 2020 14:31:27 -0700 IronPort-SDR: yu9wFQzmjUr5k9T4LttPFzX/986E+PU+0a2JvT1wc9VuuuSsTWryGQrFmD97RqGr6r+sipYwfo +NRT7opDs6tA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,411,1580803200"; d="scan'208";a="258849293" Received: from rpiazzo-mobl.amr.corp.intel.com (HELO [10.254.108.210]) ([10.254.108.210]) by orsmga006.jf.intel.com with ESMTP; 21 Apr 2020 14:31:25 -0700 Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages From: Dave Hansen 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> <396a4ece-ec66-d023-2c7e-f09f84b358bc@intel.com> 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: <396a4ece-ec66-d023-2c7e-f09f84b358bc@intel.com> 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 12:02 PM, Dave Hansen wrote: > 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. >=20 > 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. >=20 > sendfile() is probably the best example of this: >=20 > fd =3D open("/normal/ext4/file", O_RDONLY); > sendfile(socket_fd, fd, &off, count); >=20 > 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. >=20 > How does sendfile work? Did you manage to see if sendfile works (or any other operation that DMAs file-backed data without being preceded by a gup)? I suspect it's actually not that hard to fix. As long as you have a dma_ops for the devices in question either via dev->dma_ops or you add an s390 get_arch_vm_ops(), you can fix *all* the DMA sites, sendfile() included. BTW, device drivers do need to know how to use the DMA mapping API. If s390 has drivers that need to be updated, I think that's vastly preferable to incomplete hooks in core mm code.