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Zone device pages are used to represent various type of device memory managed by device drivers. Currently compound zone device pages are not supported. This is because MEMORY_DEVICE_FS_DAX pages are the only user of higher order zone device pages and have their own page reference counting. A future change will unify FS DAX reference counting with normal page reference counting rules and remove the special FS DAX reference counting. Supporting that requires compound zone device pages. Supporting compound zone device pages requires compound_head() to distinguish between head and tail pages whilst still preserving the special struct page fields that are specific to zone device pages. A tail page is distinguished by having bit zero being set in page->compound_head, with the remaining bits pointing to the head page. For zone device pages page->compound_head is shared with page->pgmap. The page->pgmap field must be common to all pages within a folio, even if the folio spans memory sections. Therefore pgmap is the same for both head and tail pages and can be moved into the folio and we can use the standard scheme to find compound_head from a tail page. Link: https://lkml.kernel.org/r/67055d772e6102accf85161d0b57b0b3944292bf.1740713401.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Balbir Singh <balbirs@nvidia.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Dan Williams <dan.j.williams@intel.com> Acked-by: David Hildenbrand <david@redhat.com> Tested-by: Alison Schofield <alison.schofield@intel.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Asahi Lina <lina@asahilina.net> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Chunyan Zhang <zhang.lyra@gmail.com> Cc: "Darrick J. Wong" <djwong@kernel.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jan Kara <jack@suse.cz> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: John Hubbard <jhubbard@nvidia.com> Cc: linmiaohe <linmiaohe@huawei.com> Cc: Logan Gunthorpe <logang@deltatee.com> Cc: Matthew Wilcow (Oracle) <willy@infradead.org> Cc: Michael "Camp Drill Sergeant" Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Peter Xu <peterx@redhat.com> Cc: Sven Schnelle <svens@linux.ibm.com> Cc: Ted Ts'o <tytso@mit.edu> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vishal Verma <vishal.l.verma@intel.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: WANG Xuerui <kernel@xen0n.name> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.