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ZIL: Reduce maximum size of WR_COPIED to 7.5K

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Benchmarks show that at certain write sizes range lock/unlock take
not so much time as extra memory copy.  The exact threshold is not
obvious due to other overheads, but it is definitely lower than
~63KB used before.  Make it configurable, defaulting at 7.5KB,
that is 8KB of nearest malloc() size minus itx and lr structs.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15353
This commit is contained in:
Alexander Motin 2023-10-06 13:09:27 -04:00 committed by Brian Behlendorf
parent 3755cde22a
commit 9be8ddfb3c
2 changed files with 16 additions and 6 deletions
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5
man/man4/zfs.4
View File

@ -2150,6 +2150,11 @@ On very fragmented pools, lowering this
.Pq typically to Sy 36 KiB .Pq typically to Sy 36 KiB
can improve performance. can improve performance.
. .
.It Sy zil_maxcopied Ns = Ns Sy 7680 Ns B Po 7.5 KiB Pc Pq uint
This sets the maximum number of write bytes logged via WR_COPIED.
It tunes a tradeoff between additional memory copy and possibly worse log
space efficiency vs additional range lock/unlock.
.
.It Sy zil_min_commit_timeout Ns = Ns Sy 5000 Pq u64 .It Sy zil_min_commit_timeout Ns = Ns Sy 5000 Pq u64
This sets the minimum delay in nanoseconds ZIL care to delay block commit, This sets the minimum delay in nanoseconds ZIL care to delay block commit,
waiting for more records. waiting for more records.

17
module/zfs/zil.c
View File

@ -1958,26 +1958,28 @@ zil_max_log_data(zilog_t *zilog, size_t hdrsize)
/* /*
* Maximum amount of log space we agree to waste to reduce number of * Maximum amount of log space we agree to waste to reduce number of
* WR_NEED_COPY chunks to reduce zl_get_data() overhead (~12%). * WR_NEED_COPY chunks to reduce zl_get_data() overhead (~6%).
*/ */
static inline uint64_t static inline uint64_t
zil_max_waste_space(zilog_t *zilog) zil_max_waste_space(zilog_t *zilog)
{ {
return (zil_max_log_data(zilog, sizeof (lr_write_t)) / 8); return (zil_max_log_data(zilog, sizeof (lr_write_t)) / 16);
} }
/* /*
* Maximum amount of write data for WR_COPIED. For correctness, consumers * Maximum amount of write data for WR_COPIED. For correctness, consumers
* must fall back to WR_NEED_COPY if we can't fit the entire record into one * must fall back to WR_NEED_COPY if we can't fit the entire record into one
* maximum sized log block, because each WR_COPIED record must fit in a * maximum sized log block, because each WR_COPIED record must fit in a
* single log block. For space efficiency, we want to fit two records into a * single log block. Below that it is a tradeoff of additional memory copy
* max-sized log block. * and possibly worse log space efficiency vs additional range lock/unlock.
*/ */
static uint_t zil_maxcopied = 7680;
uint64_t uint64_t
zil_max_copied_data(zilog_t *zilog) zil_max_copied_data(zilog_t *zilog)
{ {
return ((zilog->zl_max_block_size - sizeof (zil_chain_t)) / 2 - uint64_t max_data = zil_max_log_data(zilog, sizeof (lr_write_t));
sizeof (lr_write_t)); return (MIN(max_data, zil_maxcopied));
} }
/* /*
@ -4226,3 +4228,6 @@ ZFS_MODULE_PARAM(zfs_zil, zil_, slog_bulk, U64, ZMOD_RW,
ZFS_MODULE_PARAM(zfs_zil, zil_, maxblocksize, UINT, ZMOD_RW, ZFS_MODULE_PARAM(zfs_zil, zil_, maxblocksize, UINT, ZMOD_RW,
"Limit in bytes of ZIL log block size"); "Limit in bytes of ZIL log block size");
ZFS_MODULE_PARAM(zfs_zil, zil_, maxcopied, UINT, ZMOD_RW,
"Limit in bytes WR_COPIED size");