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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 , "Aneesh Kumar K . V" Subject: Re: [PATCH v11 01/25] mm/gup: factor out duplicate code from four routines Message-ID: <20191218155211.emcegdp5uqgorfwe@box> References: <20191216222537.491123-1-jhubbard@nvidia.com> <20191216222537.491123-2-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191216222537.491123-2-jhubbard@nvidia.com> User-Agent: NeoMutt/20180716 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Dec 16, 2019 at 02:25:13PM -0800, John Hubbard wrote: > +static void put_compound_head(struct page *page, int refs) > +{ > + /* Do a get_page() first, in case refs == page->_refcount */ > + get_page(page); > + page_ref_sub(page, refs); > + put_page(page); > +} It's not terribly efficient. Maybe something like: VM_BUG_ON_PAGE(page_ref_count(page) < ref, page); if (refs > 2) page_ref_sub(page, refs - 1); put_page(page); ? -- Kirill A. Shutemov