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Now that we have the buffer cache using the folio API, we can extend the use of folios to allocate high order folios for multi-page buffers rather than an array of single pages that are then vmapped into a contiguous range. This creates a new type of single folio buffers that can have arbitrary order in addition to the existing multi-folio buffers made up of many single page folios that get vmapped. The single folio is for now stashed into the existing b_pages array, but that will go away entirely later in the series and remove the temporary page vs folio typing issues that only work because the two structures currently can be used largely interchangeable. The code that allocates buffers will optimistically attempt a high order folio allocation as a fast path if the buffer size is a power of two and thus fits into a folio. If this high order allocation fails, then we fall back to the existing multi-folio allocation code. This now forms the slow allocation path, and hopefully will be largely unused in normal conditions except for buffers with size that are not a power of two like larger remote xattrs. This should improve performance of large buffer operations (e.g. large directory block sizes) as we should now mostly avoid the expense of vmapping large buffers (and the vmap lock contention that can occur) as well as avoid the runtime pressure that frequently accessing kernel vmapped pages put on the TLBs. Based on a patch from Dave Chinner <dchinner@redhat.com>, but mutilated beyond recognition. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Carlos Maiolino <cem@kernel.org> |
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| kernel | ||
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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.