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When the persistent ring buffer is created from the memory returned by reserve_mem there is nothing prohibiting it to be memory mapped to user space. The memory is the same as the pages allocated by alloc_page(). The way the memory is managed by the ring buffer code is slightly different though and needs to be addressed. The persistent memory uses the page->id for its own purpose where as the user mmap buffer currently uses that for the subbuf array mapped to user space. If the buffer is a persistent buffer, use the page index into that buffer as the identifier instead of the page->id. That is, the page->id for a persistent buffer, represents the order of the buffer is in the link list. ->id == 0 means it is the reader page. When a reader page is swapped, the new reader page's ->id gets zero, and the old reader page gets the ->id of the page that it swapped with. The user space mapping has the ->id is the index of where it was mapped in user space and does not change while it is mapped. Since the persistent buffer is fixed in its location, the index of where a page is in the memory range can be used as the "id" to put in the meta page array, and it can be mapped in the same order to user space as it is in the persistent memory. A new rb_page_id() helper function is used to get and set the id depending on if the page is a normal memory allocated buffer or a physical memory mapped buffer. Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Vincent Donnefort <vdonnefort@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Mike Rapoport <rppt@kernel.org> Cc: Jann Horn <jannh@google.com> Link: https://lore.kernel.org/20250401203332.246646011@goodmis.org Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> |
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| README | ||
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.