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 pE1nu/9A 89siTgXczGmt/cXH2k0PMAaUIQjKMAjheKunYc/lA2XRh8cygXReqBBCgv64syIPPuroeeMoBZw/uucN78jhqqvg3DeqB6sAuFE+wGbYaf8xzCBSEiOMXvnPBtZNhgk2bgGnS7pj1oYcrneblE3ASc2UdMT8sHjdqYss9Ci+xcRcDaHaWqBxJhXDj41pva8ijKPy3cbmboJCQs/M36k4tGFRsae4U6JirY9tLKEzWRZYtnhzV/K5iLo9z6NZGLcxtVTmrSnCI7yMS2zBYPfS7ABCYcKeozLo4hCJo9Phzv779jJXQxWQZnqycDOgAmknFkRtLmjQUNXsqTWtNjFFabJFFQgKzLKjocXCN+605Y0pWtgiZk/e7lItwSd+9uI8AGXw48AsvIrSSqoro4ufyEbLIgUdnzGMLKCugItsWbcXJzZI+NznxxI+ixn/K1zSd3yFFGHnehQK+pV6n5VRjYAyCE1CrwBtGxBlL Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Aug 05, 2026 at 05:29:34PM +0100, Lorenzo Stoakes (ARM) wrote: > On Wed, Aug 05, 2026 at 09:15:24AM -0300, Jason Gunthorpe wrote: > > On Wed, Aug 05, 2026 at 07:55:40AM +0200, Cédric Le Goater wrote: > > > > > The result: each 256 GB BAR is mapped at 4 KiB granularity -- 67 million > > > page faults per GPU instead of a few thousand PMD/PUD faults. On hosts > > > with 8 GPUs (2 TB of BAR space), this causes VM boot times to degrade > > > severely, with 99.98% of CPU time spent in the VFIO BAR mapping path. > > > > Broadly upstream we expect people to use iommufd and dmabuf for these > > configurations to avoid all this nonsense overhead. :\ > > Point taken on that :) but I think it's generally reasonable in line with the > huge PFN map changes to do something like I suggested. Yeah, for cases like this working with pure PFNs from some non-folio source the size should be entirely delegated to the driver, and driver should always have the opportunity to place a maximally sized PTE. It is definately wrong to intermix it with any THP logic. DAX isn't a special case, it was just the first place to partially implement something that looks like this. Jason