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Shutemov" To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?utf-8?B?SsOpcsO0bWU=?= 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 , Christoph Hellwig Subject: Re: [PATCH v11 04/25] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Message-ID: <20191218160420.gyt4c45e6zsnxqv6@box> References: <20191216222537.491123-1-jhubbard@nvidia.com> <20191216222537.491123-5-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: <20191216222537.491123-5-jhubbard@nvidia.com> User-Agent: NeoMutt/20180716 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Mon, Dec 16, 2019 at 02:25:16PM -0800, 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. What the reason to separate put_devmap_managed_page() from free_devmap_managed_page() if free_devmap_managed_page() has exacly one caller? Is it preparation for the next patches? > 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. > > Cc: Christoph Hellwig > Suggested-by: Jérôme Glisse > Reviewed-by: Dan Williams > Reviewed-by: Jan Kara > Signed-off-by: Ira Weiny > Signed-off-by: John Hubbard > --- > include/linux/mm.h | 17 +++++++++++++---- > mm/memremap.c | 16 ++-------------- > mm/swap.c | 24 ++++++++++++++++++++++++ > 3 files changed, 39 insertions(+), 18 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index c97ea3b694e6..77a4df06c8a7 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -952,9 +952,10 @@ 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; > @@ -963,7 +964,6 @@ 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; > @@ -971,7 +971,14 @@ static inline bool put_devmap_managed_page(struct page *page) > return false; > } > > +bool put_devmap_managed_page(struct page *page); > + > #else /* CONFIG_DEV_PAGEMAP_OPS */ > +static inline bool page_is_devmap_managed(struct page *page) > +{ > + return false; > +} > + > static inline bool put_devmap_managed_page(struct page *page) > { > return false; > @@ -1028,8 +1035,10 @@ static inline void put_page(struct page *page) > * need to inform the device driver through callback. See > * include/linux/memremap.h and HMM for details. > */ > - if (put_devmap_managed_page(page)) > + if (page_is_devmap_managed(page)) { > + put_devmap_managed_page(page); put_devmap_managed_page() has yet another page_is_devmap_managed() check inside. It looks strange. > return; > + } > > if (put_page_testzero(page)) > __put_page(page); > diff --git a/mm/memremap.c b/mm/memremap.c > index e899fa876a62..2ba773859031 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -411,20 +411,8 @@ 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); > - > - /* still busy */ > - if (count > 1) > - return; > - > - /* only triggered by the dev_pagemap shutdown path */ > - if (count == 0) { > - __put_page(page); > - return; > - } > - > /* notify page idle for dax */ > if (!is_device_private_page(page)) { > wake_up_var(&page->_refcount); > @@ -461,5 +449,5 @@ void __put_devmap_managed_page(struct page *page) > page->mapping = NULL; > page->pgmap->ops->page_free(page); > } > -EXPORT_SYMBOL(__put_devmap_managed_page); > +EXPORT_SYMBOL(free_devmap_managed_page); > #endif /* CONFIG_DEV_PAGEMAP_OPS */ > diff --git a/mm/swap.c b/mm/swap.c > index 5341ae93861f..49f7c2eea0ba 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -1102,3 +1102,27 @@ void __init swap_setup(void) > * _really_ don't want to cluster much more > */ > } > + > +#ifdef CONFIG_DEV_PAGEMAP_OPS > +bool put_devmap_managed_page(struct page *page) > +{ > + bool is_devmap = page_is_devmap_managed(page); > + > + if (is_devmap) { Reversing the condition would save you an indentation level. > + 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; > +} > +EXPORT_SYMBOL(put_devmap_managed_page); > +#endif > -- > 2.24.1 > > -- Kirill A. Shutemov