From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761752AbcJ1QQt (ORCPT ); Fri, 28 Oct 2016 12:16:49 -0400 Received: from mail-qt0-f194.google.com ([209.85.216.194]:36350 "EHLO mail-qt0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761731AbcJ1QQr (ORCPT ); Fri, 28 Oct 2016 12:16:47 -0400 Date: Fri, 28 Oct 2016 12:16:44 -0400 From: Jerome Glisse To: "Aneesh Kumar K.V" 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 Subject: Re: [RFC 0/8] Define coherent device memory node Message-ID: <20161028161644.GB11920@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> <878tt96nxr.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <878tt96nxr.fsf@linux.vnet.ibm.com> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 28, 2016 at 10:59:52AM +0530, Aneesh Kumar K.V wrote: > 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); Like i said right now for un-addressable memory my patches are mostly broken. For read and write. I am focusing on page write back for now as it seemed to be the more problematic case. For read/write the intention is to trigger a migration back to system memory inside read/write of filesystem. This is also why i will need a flag to indicate if a filesystem support migration to un-addressable memory. But in your case where the device memory is accessible then it should just work, or do you need to do special thing when kmaping device page ? Cheers, Jérôme