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The btree bulk loading code requires that records be provided in the correct record sort order for the given btree type. In general, repair code cannot be required to collect records in order, and it is not feasible to insert new records in the middle of an array to maintain sort order. Implement a sorting algorithm so that we can sort the records just prior to bulk loading. In principle, an xfarray could consume many gigabytes of memory and its backing pages can be sent out to disk at any time. This means that we cannot map the entire array into memory at once, so we must find a way to divide the work into smaller portions (e.g. a page) that /can/ be mapped into memory. Quicksort seems like a reasonable fit for this purpose, since it uses a divide and conquer strategy to keep its average runtime logarithmic. The solution presented here is a port of the glibc implementation, which itself is derived from the median-of-three and tail call recursion strategies outlined by Sedgwick. Subsequent patches will optimize the implementation further by utilizing the kernel's heapsort on directly-mapped memory whenever possible, and improving the quicksort pivot selection algorithm to try to avoid O(n^2) collapses. Note: The sorting functionality gets its own patch because the basic big array mechanisms were plenty for a single code patch. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev> Reviewed-by: Dave Chinner <dchinner@redhat.com>
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 Restructured Text 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.