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Wysocki" , Andrew Morton , Mike Marciniszyn , Michael Guralnik , Dan Williams , Ard Biesheuvel , Valentine Sinitsyn , Lukas Wunner References: <20240605192934.742369-1-martin.oliveira@eideticom.com> <20240605192934.742369-2-martin.oliveira@eideticom.com> <2024060658-ember-unblessed-4c74@gregkh> Content-Language: en-CA From: Logan Gunthorpe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 104.157.31.28 X-SA-Exim-Rcpt-To: hch@infradead.org, gregkh@linuxfoundation.org, martin.oliveira@eideticom.com, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, jgg@ziepe.ca, leon@kernel.org, bhelgaas@google.com, tj@kernel.org, rafael@kernel.org, akpm@linux-foundation.org, mike.marciniszyn@intel.com, michaelgur@nvidia.com, dan.j.williams@intel.com, ardb@kernel.org, valesini@yandex-team.ru, lukas@wunner.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH 1/6] kernfs: create vm_operations_struct without page_mkwrite() X-SA-Exim-Version: 4.2.1 (built Wed, 06 Jul 2022 17:57:39 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) X-Stat-Signature: h7rkwfjdu88t57bkyfftwcsjb115jy6g X-Rspamd-Queue-Id: 7089DC0012 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1717777048-74922 X-HE-Meta: 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 D8mvwEoU IW1mlLKOhDTl9cLhkmQ5vsKdHcGzi+H20dZg1M2xOA7FW9W9LY7Qvg60ED5tFIscVNQ3LHueSIk8aWPwr6v1pM7v/AyEEd3i04QQJwYowRtUambhzow9Imc3yCBNGzTOcyPw5O7+O0PWq4B6EDhxFCmdELnqrfX+liW7emUw1zq/bfxOAS0a9KZT67oi5gqrm6YstURe4QyqyFF1iKB+bUYQyzrD2By8eiWxB17VGvNfRHc4UAKM+LGcyiWBVBtVv9E9tip6YytC++qFIeqwkfCMYOQaD2SlnsseK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024-06-06 23:03, Christoph Hellwig wrote: > On Thu, Jun 06, 2024 at 10:54:06PM +0200, Greg Kroah-Hartman wrote: >> On Wed, Jun 05, 2024 at 01:29:29PM -0600, Martin Oliveira wrote: >>> The standard kernfs vm_ops installs a page_mkwrite() operator which >>> modifies the file update time on write. >>> >>> This not always required (or makes sense), such as in the P2PDMA, which >>> uses the sysfs file as an allocator from userspace. >> >> That's not a good idea, please don't do that. sysfs binary files are >> "pass through", why would you want to use this as an allocator? > > I think the real question is why sysfs binary files implement > page_mkwrite by default. page_mkwrite is needed for file systems that > need to allocate space from a free space pool, which seems odd for > sysfs. The default page_mkwrite in kernfs just calls file_update_time() but, as I understand it, the fault code should call file_update_time() if page_mkwrite isn't set. So perhaps the easiest thing is to simply not add a page_mkwrite unless the vm_ops adds one. It's not the easiest thing to trace, but as best as I can tell there are no kernfs binary attributes that use page_mkwrite. So alternatively, perhaps we could just disallow page_mkwrite in kernfs entirely? Logan