From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1949243AbdD1SAP convert rfc822-to-8bit (ORCPT ); Fri, 28 Apr 2017 14:00:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36082 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1426551AbdD1SAN (ORCPT ); Fri, 28 Apr 2017 14:00:13 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 606DA25BF6E Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jglisse@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 606DA25BF6E Date: Fri, 28 Apr 2017 14:00:06 -0400 (EDT) From: Jerome Glisse To: Dan Williams Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Linux MM , Ingo Molnar , Andrew Morton , Logan Gunthorpe , Kirill Shutemov Message-ID: <1579714997.4315035.1493402406629.JavaMail.zimbra@redhat.com> In-Reply-To: References: <20170428063913.iz6xjcxblecofjlq@gmail.com> <149339998297.24933.1129582806028305912.stgit@dwillia2-desk3.amr.corp.intel.com> <1743017574.4309811.1493400875692.JavaMail.zimbra@redhat.com> Subject: Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.10.126.32, 10.4.195.1] Thread-Topic: mm, zone_device: replace {get, put}_zone_device_page() with a single reference Thread-Index: /OksbuzDSITPb51/xzQUJa6VEJpSiQ== X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Fri, 28 Apr 2017 18:00:12 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Fri, Apr 28, 2017 at 10:34 AM, Jerome Glisse wrote: > >> Kirill points out that the calls to {get,put}_dev_pagemap() can be > >> removed from the mm fast path if we take a single get_dev_pagemap() > >> reference to signify that the page is alive and use the final put of the > >> page to drop that reference. > >> > >> This does require some care to make sure that any waits for the > >> percpu_ref to drop to zero occur *after* devm_memremap_page_release(), > >> since it now maintains its own elevated reference. > > > > This is NAK from HMM point of view as i need those call. So if you remove > > them now i will need to add them back as part of HMM. > > I thought you only need them at page free time? You can still hook > __put_page(). No, i need a hook when page refcount reach 1, not 0. That being said i don't care about put_dev_pagemap(page->pgmap); so that part of the patch is fine from HMM point of view but i definitly need to hook my- self in the general put_page() function. So i will have to undo part of this patch for HMM (put_page() will need to handle ZONE_DEVICE page differently). Cheers, Jérôme