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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: <20240605214342.GA781723@bhelgaas> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240605192934.742369-2-martin.oliveira@eideticom.com> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 64D2110000B X-Stat-Signature: ftp9rdhpbwyw7ikq36y5ijtxhtdhwt63 X-HE-Tag: 1717623826-528691 X-HE-Meta: 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 QnEys/FK lMhXgi0Rv03tZKjYDsnKyE2ZRT4J8IG17wJvmPoVd4cPmNAWN6SD35pvGdzHlnaka/9vL/ALFS8t8aaex5dR7AjP+4rf0gl+8lMGykUTjj808NK6py0J1xbRl6u/23x57K58cvz1PqPIEWw+TRcyQIQf8peGYhEkI0ebzszYA2bXhgF0GpMROFin97L5s43Jqvi/tZcxWVhgp34KqA7NlkFtBq+9ZixEmKfWxjKHdrShfA28= 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 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 s/This/This is/ ? > uses the sysfs file as an allocator from userspace. > > Furthermore, having the page_mkwrite() operator causes > writable_file_mapping_allowed() to fail due to > vma_needs_dirty_tracking() on the gup flow, which is a pre-requisite for > enabling P2PDMA over RDMA. > > Fix this by adding a new boolean on kernfs_ops to differentiate between > the different behaviours. > + * Use the file as an allocator from userspace. This disables > + * page_mkwrite() to prevent the file time from being updated on write > + * which enables using GUP with FOLL_LONGTERM with memory that's been > + * mmaped. "mmaped" does seem more commonly used in Linux than "mmapped", but the base word "mapped" definitely requires "pp", so "mmaped" looks funny to me.