Alexander Motin 9a81484e35 ZAP: Reduce leaf array and free chunks fragmentation
Previous implementation of zap_leaf_array_free() put chunks on the
free list in reverse order.  Also zap_leaf_transfer_entry() and
zap_entry_remove() were freeing name and value arrays in reverse
order.  Together this created a mess in the free list, making
following allocations much more fragmented than necessary.

This patch re-implements zap_leaf_array_free() to keep existing
chunks order, and implements non-destructive zap_leaf_array_copy()
to be used in zap_leaf_transfer_entry() to allow properly ordered
freeing name and value arrays there and in zap_entry_remove().

With this change test of some writes and deletes shows percent of
non-contiguous chunks in DDT reducing from 61% and 47% to 0% and
17% for arrays and frees respectively.  Sure some explicit sorting
could do even better, especially for ZAPs with variable-size arrays,
but it would also cost much more, while this should be very cheap.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #16766
2024-11-20 13:37:52 -08:00
2022-12-22 11:34:28 -08:00
2020-06-09 21:24:09 -07:00
2018-05-29 16:00:33 -07:00
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2020-08-26 21:44:41 -07:00
2018-05-29 16:00:33 -07:00
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2020-03-16 10:46:03 -07:00

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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.

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Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.

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We have a separate document with contribution guidelines.

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OpenZFS is released under a CDDL license. For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197

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  • The META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.
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