From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1034068AbdD0QMD (ORCPT ); Thu, 27 Apr 2017 12:12:03 -0400 Received: from ale.deltatee.com ([207.54.116.67]:57095 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032672AbdD0QLy (ORCPT ); Thu, 27 Apr 2017 12:11:54 -0400 To: Dan Williams , akpm@linux-foundation.org References: <20170423233125.nehmgtzldgi25niy@node.shutemov.name> <149325431313.40660.7404075559824162131.stgit@dwillia2-desk3.amr.corp.intel.com> Cc: linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , linux-kernel@vger.kernel.org, Kirill Shutemov From: Logan Gunthorpe Message-ID: <3e595ba6-2ea1-e25d-e254-6c7edcf23f88@deltatee.com> Date: Thu, 27 Apr 2017 10:11:46 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <149325431313.40660.7404075559824162131.stgit@dwillia2-desk3.amr.corp.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.111 X-SA-Exim-Rcpt-To: kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org, jglisse@redhat.com, linux-mm@kvack.org, akpm@linux-foundation.org, dan.j.williams@intel.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:24:06 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/04/17 06:55 PM, Dan Williams wrote: > @@ -277,7 +269,10 @@ struct dev_pagemap *find_dev_pagemap(resource_size_t phys) > * > * Notes: > * 1/ @ref must be 'live' on entry and 'dead' before devm_memunmap_pages() time > - * (or devm release event). > + * (or devm release event). The expected order of events is that @ref has > + * been through percpu_ref_kill() before devm_memremap_pages_release(). The > + * wait for the completion of kill and percpu_ref_exit() must occur after > + * devm_memremap_pages_release(). > * > * 2/ @res is expected to be a host memory range that could feasibly be > * treated as a "System RAM" range, i.e. not a device mmio range, but > @@ -379,6 +374,7 @@ void *devm_memremap_pages(struct device *dev, struct resource *res, > */ > list_del(&page->lru); > page->pgmap = pgmap; > + percpu_ref_get(ref); > } > devres_add(dev, page_map); > return __va(res->start); > diff --git a/mm/swap.c b/mm/swap.c > index 5dabf444d724..01267dda6668 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -97,6 +97,16 @@ static void __put_compound_page(struct page *page) > > void __put_page(struct page *page) > { > + if (is_zone_device_page(page)) { > + put_dev_pagemap(page->pgmap); > + > + /* > + * The page belong to device, do not return it to > + * page allocator. > + */ > + return; > + } > + > if (unlikely(PageCompound(page))) > __put_compound_page(page); > else > Forgive me if I'm missing something but this doesn't make sense to me. We are taking a reference once when the region is initialized and releasing it every time a page within the region's reference count drops to zero. That does not seem to be symmetric and I don't see how it tracks that pages are in use. Shouldn't get_dev_pagemap be called when any page is allocated or something like that (ie. the inverse of __put_page)? Thanks, Logan