xfs: improve xfarray quicksort pivot

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Now that we have the means to do insertion sorts of small in-memory
subsets of an xfarray, use it to improve the quicksort pivot algorithm
by reading 7 records into memory and finding the median of that.  This
should prevent bad partitioning when a[lo] and a[hi] end up next to each
other in the final sort, which can happen when sorting for cntbt repair
when the free space is extremely fragmented (e.g. generic/176).

This doesn't speed up the average quicksort run by much, but it will
(hopefully) avoid the quadratic time collapse for which quicksort is
famous.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

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Darrick J. Wong 2023-08-10 07:48:07 -07:00

parent cf36f4f64c

commit 764018caa9

2 changed files with 148 additions and 69 deletions

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210

fs/xfs/scrub/xfarray.c

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19

fs/xfs/scrub/xfarray.h

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