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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id z3sm583141qkf.92.2020.09.17.13.25.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2020 13:25:15 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kJ0Sw-000lSJ-U4; Thu, 17 Sep 2020 17:25:14 -0300 Date: Thu, 17 Sep 2020 17:25:14 -0300 From: Jason Gunthorpe To: John Hubbard Cc: Linus Torvalds , Peter Xu , Leon Romanovsky , Linux-MM , Linux Kernel Mailing List , "Maya B . Gokhale" , Yang Shi , Marty Mcfadden , Kirill Shutemov , Oleg Nesterov , Jann Horn , Jan Kara , Kirill Tkhai , Andrea Arcangeli , Christoph Hellwig , Andrew Morton Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification Message-ID: <20200917202514.GN8409@ziepe.ca> References: <20200916174804.GC8409@ziepe.ca> <20200916184619.GB40154@xz-x1> <20200917112538.GD8409@ziepe.ca> <20200917181411.GA133226@xz-x1> <20200917190332.GB133226@xz-x1> <20200917200638.GM8409@ziepe.ca> <24b8ad6b-4e4c-4651-86e6-bc2232fce772@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <24b8ad6b-4e4c-4651-86e6-bc2232fce772@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 17, 2020 at 01:19:02PM -0700, John Hubbard wrote: > On 9/17/20 1:06 PM, Jason Gunthorpe wrote: > > On Thu, Sep 17, 2020 at 12:42:11PM -0700, Linus Torvalds wrote: > ... > > > Is there possibly somethign else we can filter on than just > > > GUP_PIN_COUNTING_BIAS? Because it could be as simple as just marking > > > the vma itself and saying "this vma has had a page pinning event done > > > on it". > > > > We'd have to give up pin_user_pages_fast() to do that as we can't fast > > walk and get vmas? > > oops, yes. I'd forgotten about that point. Basically all of the O_DIRECT > callers need _fast. This is a big problem. What about an atomic counter in the mm_struct? # of pages currently under pin. The use case Linus is worried about will never have any pins, so it would be 0 and it could skip this entire test. Jason