Alexander Motin dc91a6a660 Several B-tree optimizations
- Introduce first element offset within a leaf.  It allows to reduce
by ~50% average memmove() size when adding/removing elements.  If the
added/removed element is in the first half of the leaf, we may shift
elements before it and adjust the bth_first instead of moving more
elements after it.
 - Use memcpy() instead of memmove() when we know there is no overlap.
 - Switch from uint64_t to uint32_t.  It does not limit anything,
but 32-bit arches should appreciate it greatly in hot paths.
 - Store leaf capacity in struct btree to avoid 64-bit divisions.
 - Adjust zfs_btree_insert_into_leaf() to always result in balanced
leaves after splitting, no matter where the new element was inserted.
Not that we care about it much, but it should also allow B-trees with
as little as two elements per leaf instead of 4 previously.

When scrubbing pool of 12 SSDs, storing 1.5TB of 4KB zvol blocks this
reduces amount of time spent in memmove() inside the scan thread from
13.7% to 5.7% and total scrub time by ~15 seconds out of 9 minutes.
It should also reduce spacemaps load time, but I haven't measured it.

Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored-By: iXsystems, Inc.
Closes #13582
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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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Official Resources

Installation

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

Contribute & Develop

We have a separate document with contribution guidelines.

We have a Code of Conduct.

Release

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

Supported Kernels

  • The META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are any supported branches and releases starting from 12.2-RELEASE.
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