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8db00ad564
As long as the owner sets a page type first, we can allow reuse of the lower 16 bit: sufficient to store an offset into a 64 KiB page, which is the maximum base page size in *common* configurations (ignoring the 256 KiB variant). Restrict it to the head page. We'll use that for zsmalloc next, to set a proper type while still reusing that field to store information (offset into a base page) that cannot go elsewhere for now. Let's reserve the lower 16 bit for that purpose and for catching mapcount underflows, and let's reduce PAGE_TYPE_BASE to a single bit. Note that we will still have to overflow the mapcount quite a lot until we would actually indicate a valid page type. Start handing out the type bits from highest to lowest, to make it clearer how many bits for types we have left. Out of 15 bit we can use for types, we currently use 6. If we run out of bits before we have better typing (e.g., memdesc), we can always investigate storing a value instead [1]. [1] https://lore.kernel.org/all/00ba1dff-7c05-46e8-b0d9-a78ac1cfc198@redhat.com/ [akpm@linux-foundation.org: fix PG_hugetlb typo, per David] Link: https://lkml.kernel.org/r/20240529111904.2069608-3-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Tested-by: Sergey Senozhatsky <senozhatsky@chromium.org> [zram/zsmalloc workloads] Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Minchan Kim <minchan@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.