From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id 1AA826B027A for ; Fri, 28 Oct 2016 03:35:46 -0400 (EDT) Received: by mail-pa0-f69.google.com with SMTP id fl2so38700465pad.7 for ; Fri, 28 Oct 2016 00:35:46 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id n67si12236568pga.91.2016.10.28.00.35.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Oct 2016 00:35:45 -0700 (PDT) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u9S7XsAf124804 for ; Fri, 28 Oct 2016 03:35:44 -0400 Received: from e31.co.us.ibm.com (e31.co.us.ibm.com [32.97.110.149]) by mx0b-001b2d01.pphosted.com with ESMTP id 26bvbygfjh-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 28 Oct 2016 03:35:44 -0400 Received: from localhost by e31.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 28 Oct 2016 01:35:43 -0600 From: "Aneesh Kumar K.V" Subject: Re: [RFC 0/8] Define coherent device memory node In-Reply-To: <20161026160721.GA13638@gmail.com> References: <1477283517-2504-1-git-send-email-khandual@linux.vnet.ibm.com> <20161024170902.GA5521@gmail.com> <87a8dtawas.fsf@linux.vnet.ibm.com> <20161025151637.GA6072@gmail.com> <87y41bcqow.fsf@linux.vnet.ibm.com> <20161026160721.GA13638@gmail.com> Date: Fri, 28 Oct 2016 10:59:52 +0530 MIME-Version: 1.0 Content-Type: text/plain Message-Id: <878tt96nxr.fsf@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: Anshuman Khandual , linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, js1304@gmail.com, vbabka@suse.cz, mgorman@suse.de, minchan@kernel.org, akpm@linux-foundation.org, bsingharora@gmail.com Jerome Glisse writes: > On Wed, Oct 26, 2016 at 04:39:19PM +0530, Aneesh Kumar K.V wrote: >> Jerome Glisse writes: >> >> > On Tue, Oct 25, 2016 at 09:56:35AM +0530, Aneesh Kumar K.V wrote: >> >> Jerome Glisse writes: >> >> >> >> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote: >> >> > >> >> I looked at the hmm-v13 w.r.t migration and I guess some form of device >> >> callback/acceleration during migration is something we should definitely >> >> have. I still haven't figured out how non addressable and coherent device >> >> memory can fit together there. I was waiting for the page cache >> >> migration support to be pushed to the repository before I start looking >> >> at this closely. >> >> >> > >> > The page cache migration does not touch the migrate code path. My issue with >> > page cache is writeback. The only difference with existing migrate code is >> > refcount check for ZONE_DEVICE page. Everything else is the same. >> >> What about the radix tree ? does file system migrate_page callback handle >> replacing normal page with ZONE_DEVICE page/exceptional entries ? >> > > It use the exact same existing code (from mm/migrate.c) so yes the radix tree > is updated and buffer_head are migrated. > I looked at the the page cache migration patches shared and I find that you are not using exceptional entries when we migrate a page cache page to device memory. But I am now not sure how a read from page cache will work with that. ie, a file system read will now find the page in page cache. But we cannot do a copy_to_user of that page because that is now backed by an unaddressable memory right ? do_generic_file_read() does page = find_get_page(mapping, index); .... ret = copy_page_to_iter(page, offset, nr, iter); which does void *kaddr = kmap_atomic(page); size_t wanted = copy_to_iter(kaddr + offset, bytes, i); kunmap_atomic(kaddr); -aneesh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org