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[23.128.96.18]) by mx.google.com with ESMTP id a14si2376579edn.58.2020.04.16.13.28.25; Thu, 16 Apr 2020 13:28:48 -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 S2394421AbgDPOd1 (ORCPT + 99 others); Thu, 16 Apr 2020 10:33:27 -0400 Received: from mga18.intel.com ([134.134.136.126]:28772 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391699AbgDPOUu (ORCPT ); Thu, 16 Apr 2020 10:20:50 -0400 IronPort-SDR: Yl/9Vwme6a2z4ZfinLTkn45Gx9ADKvcdn30GCYpXZR+4WdnDc64ageH4whe/UrYPbyxLvUZtST WoTSG/cJLAzA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Apr 2020 07:20:49 -0700 IronPort-SDR: 4aXlHZMbhNG1je7pcHHUeeCakUi0Jtdz4mAIIAD/SttvwL4xTsvtfe3yBUnis54lyriFtIAJpN Rn8JSuP7HYrw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,391,1580803200"; d="scan'208";a="257231281" 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 07:20:48 -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> 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: <20200416141547.29be5ea0@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 5:15 AM, Claudio Imbrenda wrote: >> I assumed that this was all anonymous-only so it's always dirty before >> writeback starts. > it could also be mmapped Let's say you have a mmap()'d ramfs file. Another process calls which doesn't have it mapped calls sys_write() and writes to the file. This means that host host has to write to the physical page and must do arch_make_page_accessible() in the sys_write() path somewhere. There is a get_user_pages() in that path, but it's on the _source_ buffer, not the ramfs page because the ramfs page is not mapped. There's also no __test_set_page_writeback() because you can't write back ramfs. Where is the arch_make_page_accessible() in this case on the ramfs page?