freebsd-nq/module
Matthew Ahrens be89734a29 compress metadata in later sync passes
Starting in sync pass 5 (zfs_sync_pass_dont_compress), we disable
compression (including of metadata).  Ostensibly this helps the sync
passes to converge (i.e. for a sync pass to not need to allocate
anything because it is 100% overwrites).

However, in practice it increases the average number of sync passes,
because when we turn compression off, a lot of block's size will change
and thus we have to re-allocate (not overwrite) them.  It also increases
the number of 128KB allocations (e.g. for indirect blocks and spacemaps)
because these will not be compressed.  The 128K allocations are
especially detrimental to performance on highly fragmented systems,
which may have very few free segments of this size, and may need to load
new metaslabs to satisfy 128K allocations.

We should increase zfs_sync_pass_dont_compress.  In practice on a highly
fragmented system we see a few 5-pass txg's, a tiny number of 6-pass
txg's, and no txg's with more than 6 passes.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-63431
Closes #8892
2019-06-13 13:10:18 -07:00
..
avl Update build system and packaging 2018-05-29 16:00:33 -07:00
icp Restructure vec_idx loops 2019-04-16 12:34:06 -07:00
lua Update build system and packaging 2018-05-29 16:00:33 -07:00
nvpair Use NV_ENCODE_NATIVE for nvlist encoding variable 2019-04-26 11:24:31 -07:00
spl Remove vn_set_fs_pwd()/vn_set_pwd() (no need to be at / during insmod) 2019-05-29 16:18:14 -07:00
unicode Update build system and packaging 2018-05-29 16:00:33 -07:00
zcommon Restrict filesystem creation if name referred either '.' or '..' 2019-06-13 08:56:15 -07:00
zfs compress metadata in later sync passes 2019-06-13 13:10:18 -07:00
.gitignore Prepare SPL repo to merge with ZFS repo 2018-05-29 14:51:39 -07:00
Makefile.in Linux 5.0 compat: Fix SUBDIRs 2019-01-28 10:11:45 -08:00