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Alistair Popple
aed877c2b4
Device DAX pages are currently not reference counted when mapped, instead relying on the devmap PTE bit to ensure mapping code will not get/put references. This requires special handling in various page table walkers, particularly GUP, to manage references on the underlying pgmap to ensure the pages remain valid. However there is no reason these pages can't be refcounted properly at map time. Doning so eliminates the need for the devmap PTE bit, freeing up a precious PTE bit. It also simplifies GUP as it no longer needs to manage the special pgmap references and can instead just treat the pages normally as defined by vm_normal_page(). Link: https://lkml.kernel.org/r/968d3a8e9157e7492e85d065765c027e525f9fc9.1740713401.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple <[email protected]> Tested-by: Alison Schofield <[email protected]> Cc: Alexander Gordeev <[email protected]> Cc: Asahi Lina <[email protected]> Cc: Balbir Singh <[email protected]> Cc: Bjorn Helgaas <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Christian Borntraeger <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Chunyan Zhang <[email protected]> Cc: Dan Wiliams <[email protected]> Cc: "Darrick J. Wong" <[email protected]> Cc: Dave Chinner <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Dave Jiang <[email protected]> Cc: David Hildenbrand <[email protected]> Cc: Gerald Schaefer <[email protected]> Cc: Heiko Carstens <[email protected]> Cc: Huacai Chen <[email protected]> Cc: Ira Weiny <[email protected]> Cc: Jan Kara <[email protected]> Cc: Jason Gunthorpe <[email protected]> Cc: Jason Gunthorpe <[email protected]> Cc: John Hubbard <[email protected]> Cc: linmiaohe <[email protected]> Cc: Logan Gunthorpe <[email protected]> Cc: Matthew Wilcow (Oracle) <[email protected]> Cc: Michael "Camp Drill Sergeant" Ellerman <[email protected]> Cc: Nicholas Piggin <[email protected]> Cc: Peter Xu <[email protected]> Cc: Sven Schnelle <[email protected]> Cc: Ted Ts'o <[email protected]> Cc: Vasily Gorbik <[email protected]> Cc: Vishal Verma <[email protected]> Cc: Vivek Goyal <[email protected]> Cc: WANG Xuerui <[email protected]> Cc: Will Deacon <[email protected]> Signed-off-by: Andrew Morton <[email protected]>