From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f200.google.com (mail-io0-f200.google.com [209.85.223.200]) by kanga.kvack.org (Postfix) with ESMTP id 3C3CB6B02FA for ; Thu, 27 Apr 2017 12:11:53 -0400 (EDT) Received: by mail-io0-f200.google.com with SMTP id h41so15197501ioi.1 for ; Thu, 27 Apr 2017 09:11:53 -0700 (PDT) Received: from ale.deltatee.com (ale.deltatee.com. [207.54.116.67]) by mx.google.com with ESMTPS id i129si5942436itd.43.2017.04.27.09.11.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Apr 2017 09:11:52 -0700 (PDT) References: <20170423233125.nehmgtzldgi25niy@node.shutemov.name> <149325431313.40660.7404075559824162131.stgit@dwillia2-desk3.amr.corp.intel.com> From: Logan Gunthorpe Message-ID: <3e595ba6-2ea1-e25d-e254-6c7edcf23f88@deltatee.com> Date: Thu, 27 Apr 2017 10:11:46 -0600 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 Subject: Re: [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams , akpm@linux-foundation.org Cc: linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , linux-kernel@vger.kernel.org, Kirill Shutemov 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 -- 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