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[23.128.96.18]) by mx.google.com with ESMTP id gq24si12522299ejb.222.2020.04.16.14.24.53; Thu, 16 Apr 2020 14:25:16 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730139AbgDPTC5 (ORCPT + 99 others); Thu, 16 Apr 2020 15:02:57 -0400 Received: from mga01.intel.com ([192.55.52.88]:19476 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727800AbgDPTC4 (ORCPT ); Thu, 16 Apr 2020 15:02:56 -0400 IronPort-SDR: o8/lOeAnBe/FfP/a6aJ68/Xzx2pXIw5MSULeFsS1IObvMn9MiGyfkgMfHImZG27VkAzEuysfcK bbUfLvaejs+A== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 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: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 = 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?