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Patch series "mm: page_type, zsmalloc and page_mapcount_reset()", v2. Wanting to remove the remaining abuser of _mapcount/page_type along with page_mapcount_reset(), I stumbled over zsmalloc, which is yet to be converted away from "struct page" [1]. Unfortunately, we cannot stop using the page_type field in zsmalloc code completely for its own purposes. All other fields in "struct page" are used one way or the other. Could we simply store a 2-byte offset value at the beginning of each page? Likely, but that will require a bit more work; and once we have memdesc we might want to move the offset in there (struct zsalloc?) again. ... but we can limit the abuse to 16 bit, glue it to a page type that must be set, and document it. page_has_type() will always successfully indicate such zsmalloc pages, and such zsmalloc pages only. We lose zsmalloc support for PAGE_SIZE > 64KB, which should be tolerable. We could use more bits from the page type, but 16 bit sounds like a good idea for now. So clarify the _mapcount/page_type documentation, use a proper page_type for zsmalloc, and remove page_mapcount_reset(). [1] https://lore.kernel.org/all/20231130101242.2590384-1-42.hyeyoo@gmail.com/ This patch (of 6): Let's make it clearer that _mapcount must no longer be used for own purposes, and how _mapcount and page_type behaves nowadays (also in the context of hugetlb folios, which are typed folios that will be mapped to user space). Move the documentation regarding "-1" over from page_mapcount_reset(), which we will remove next. Move "page_type" before "mapcount", to make it clearer what typed folios are. Link: https://lkml.kernel.org/r/20240529111904.2069608-1-david@redhat.com Link: https://lkml.kernel.org/r/20240529111904.2069608-2-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
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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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.