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Wysocki" , Andrew Morton , Mike Marciniszyn , Michael Guralnik , Dan Williams , Ard Biesheuvel , Valentine Sinitsyn , Lukas Wunner Subject: Re: [PATCH 1/6] kernfs: create vm_operations_struct without page_mkwrite() Message-ID: <2024060755-stimuli-unworthy-61a8@gregkh> References: <20240605192934.742369-1-martin.oliveira@eideticom.com> <20240605192934.742369-2-martin.oliveira@eideticom.com> <2024060658-ember-unblessed-4c74@gregkh> <69dc6610-e70a-46ca-a6e9-7ca183eb055c@deltatee.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69dc6610-e70a-46ca-a6e9-7ca183eb055c@deltatee.com> X-Rspamd-Queue-Id: B1A142000D X-Stat-Signature: ih7sbfoyro37nai94ep9tywb1hfynich X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1717787887-380327 X-HE-Meta: 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 pkrH4QF6 olIjqDWp9Rzr5XAlsoTO5ZTpG9Lb/kP3ftfk3trno4fzW+ujAI9QMawQYO86G4aSY2P4Et1SO8zPL4C/fbHG/vul+9yN8Ug2WNs5gIShsQa4MAAmIegTTCeD0iLI8ddZX+KZoa1fEBP6rk2viOXm9hVyGaqJCfTZ6kgSdgyLSDPFjhsXOZjA3G5VGTGbtUXxRFhYCNwKZ2/tVNrvn2BxZ+2NoP+Rnj1UVRCglT4xXtTJECRoQYuG7G8XcsLXLcbr8topKuBiHfruNYYc= 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 Fri, Jun 07, 2024 at 10:16:58AM -0600, Logan Gunthorpe wrote: > > > 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? Sure, let's do that.