From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CCFB3C17442 for ; Wed, 13 Nov 2019 10:49:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A66CB222D0 for ; Wed, 13 Nov 2019 10:49:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727344AbfKMKtZ (ORCPT ); Wed, 13 Nov 2019 05:49:25 -0500 Received: from mx2.suse.de ([195.135.220.15]:33058 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726138AbfKMKtZ (ORCPT ); Wed, 13 Nov 2019 05:49:25 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id B5441B20D; Wed, 13 Nov 2019 10:49:20 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 1B6A71E1498; Wed, 13 Nov 2019 11:49:20 +0100 (CET) Date: Wed, 13 Nov 2019 11:49:20 +0100 From: Jan Kara To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML Subject: Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Message-ID: <20191113104920.GF6367@quack2.suse.cz> References: <20191113042710.3997854-1-jhubbard@nvidia.com> <20191113042710.3997854-5-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20191113042710.3997854-5-jhubbard@nvidia.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue 12-11-19 20:26:51, John Hubbard wrote: > An upcoming patch changes and complicates the refcounting and > especially the "put page" aspects of it. In order to keep > everything clean, refactor the devmap page release routines: > > * Rename put_devmap_managed_page() to page_is_devmap_managed(), > and limit the functionality to "read only": return a bool, > with no side effects. > > * Add a new routine, put_devmap_managed_page(), to handle checking > what kind of page it is, and what kind of refcount handling it > requires. > > * Rename __put_devmap_managed_page() to free_devmap_managed_page(), > and limit the functionality to unconditionally freeing a devmap > page. > > This is originally based on a separate patch by Ira Weiny, which > applied to an early version of the put_user_page() experiments. > Since then, Jérôme Glisse suggested the refactoring described above. > > Suggested-by: Jérôme Glisse > Signed-off-by: Ira Weiny > Signed-off-by: John Hubbard Looks good to me. You can add: Reviewed-by: Jan Kara Honza > --- > include/linux/mm.h | 27 ++++++++++++++++--- > mm/memremap.c | 67 ++++++++++++++++++++-------------------------- > 2 files changed, 53 insertions(+), 41 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a2adf95b3f9c..96228376139c 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struct page *page) > #endif > > #ifdef CONFIG_DEV_PAGEMAP_OPS > -void __put_devmap_managed_page(struct page *page); > +void free_devmap_managed_page(struct page *page); > DECLARE_STATIC_KEY_FALSE(devmap_managed_key); > -static inline bool put_devmap_managed_page(struct page *page) > + > +static inline bool page_is_devmap_managed(struct page *page) > { > if (!static_branch_unlikely(&devmap_managed_key)) > return false; > @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct page *page) > switch (page->pgmap->type) { > case MEMORY_DEVICE_PRIVATE: > case MEMORY_DEVICE_FS_DAX: > - __put_devmap_managed_page(page); > return true; > default: > break; > @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct page *page) > return false; > } > > +static inline bool put_devmap_managed_page(struct page *page) > +{ > + bool is_devmap = page_is_devmap_managed(page); > + > + if (is_devmap) { > + int count = page_ref_dec_return(page); > + > + /* > + * devmap page refcounts are 1-based, rather than 0-based: if > + * refcount is 1, then the page is free and the refcount is > + * stable because nobody holds a reference on the page. > + */ > + if (count == 1) > + free_devmap_managed_page(page); > + else if (!count) > + __put_page(page); > + } > + > + return is_devmap; > +} > + > #else /* CONFIG_DEV_PAGEMAP_OPS */ > static inline bool put_devmap_managed_page(struct page *page) > { > diff --git a/mm/memremap.c b/mm/memremap.c > index 03ccbdfeb697..bc7e2a27d025 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn, > EXPORT_SYMBOL_GPL(get_dev_pagemap); > > #ifdef CONFIG_DEV_PAGEMAP_OPS > -void __put_devmap_managed_page(struct page *page) > +void free_devmap_managed_page(struct page *page) > { > - int count = page_ref_dec_return(page); > + /* Clear Active bit in case of parallel mark_page_accessed */ > + __ClearPageActive(page); > + __ClearPageWaiters(page); > + > + mem_cgroup_uncharge(page); > > /* > - * If refcount is 1 then page is freed and refcount is stable as nobody > - * holds a reference on the page. > + * When a device_private page is freed, the page->mapping field > + * may still contain a (stale) mapping value. For example, the > + * lower bits of page->mapping may still identify the page as > + * an anonymous page. Ultimately, this entire field is just > + * stale and wrong, and it will cause errors if not cleared. > + * One example is: > + * > + * migrate_vma_pages() > + * migrate_vma_insert_page() > + * page_add_new_anon_rmap() > + * __page_set_anon_rmap() > + * ...checks page->mapping, via PageAnon(page) call, > + * and incorrectly concludes that the page is an > + * anonymous page. Therefore, it incorrectly, > + * silently fails to set up the new anon rmap. > + * > + * For other types of ZONE_DEVICE pages, migration is either > + * handled differently or not done at all, so there is no need > + * to clear page->mapping. > */ > - if (count == 1) { > - /* Clear Active bit in case of parallel mark_page_accessed */ > - __ClearPageActive(page); > - __ClearPageWaiters(page); > - > - mem_cgroup_uncharge(page); > - > - /* > - * When a device_private page is freed, the page->mapping field > - * may still contain a (stale) mapping value. For example, the > - * lower bits of page->mapping may still identify the page as > - * an anonymous page. Ultimately, this entire field is just > - * stale and wrong, and it will cause errors if not cleared. > - * One example is: > - * > - * migrate_vma_pages() > - * migrate_vma_insert_page() > - * page_add_new_anon_rmap() > - * __page_set_anon_rmap() > - * ...checks page->mapping, via PageAnon(page) call, > - * and incorrectly concludes that the page is an > - * anonymous page. Therefore, it incorrectly, > - * silently fails to set up the new anon rmap. > - * > - * For other types of ZONE_DEVICE pages, migration is either > - * handled differently or not done at all, so there is no need > - * to clear page->mapping. > - */ > - if (is_device_private_page(page)) > - page->mapping = NULL; > + if (is_device_private_page(page)) > + page->mapping = NULL; > > - page->pgmap->ops->page_free(page); > - } else if (!count) > - __put_page(page); > + page->pgmap->ops->page_free(page); > } > -EXPORT_SYMBOL(__put_devmap_managed_page); > +EXPORT_SYMBOL(free_devmap_managed_page); > #endif /* CONFIG_DEV_PAGEMAP_OPS */ > -- > 2.24.0 > -- Jan Kara SUSE Labs, CR