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metaslab: tuneable to better control force ganging #15088

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Jul 21, 2023
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metaslab: tuneable to better control force ganging #15088

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7 changes: 6 additions & 1 deletion man/man4/zfs.4
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
.\" own identifying information:
.\" Portions Copyright [yyyy] [name of copyright owner]
.\"
.Dd January 10, 2023
.Dd July 21, 2023
.Dt ZFS 4
.Os
.
Expand Down Expand Up @@ -239,6 +239,11 @@ relative to the pool.
Make some blocks above a certain size be gang blocks.
This option is used by the test suite to facilitate testing.
.
.It Sy metaslab_force_ganging_pct Ns = Ns Sy 3 Ns % Pq uint
For blocks that could be forced to be a gang block (due to
.Sy metaslab_force_ganging ) ,
force this many of them to be gang blocks.
.
.It Sy zfs_ddt_zap_default_bs Ns = Ns Sy 15 Po 32 KiB Pc Pq int
Default DDT ZAP data block size as a power of 2. Note that changing this after
creating a DDT on the pool will not affect existing DDTs, only newly created
Expand Down
14 changes: 12 additions & 2 deletions module/zfs/metaslab.c
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Expand Up @@ -58,6 +58,11 @@ static uint64_t metaslab_aliquot = 1024 * 1024;
*/
uint64_t metaslab_force_ganging = SPA_MAXBLOCKSIZE + 1;

/*
* Of blocks of size >= metaslab_force_ganging, actually gang them this often.
*/
uint_t metaslab_force_ganging_pct = 3;

/*
* In pools where the log space map feature is not enabled we touch
* multiple metaslabs (and their respective space maps) with each
Expand Down Expand Up @@ -5109,7 +5114,9 @@ metaslab_alloc_dva(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
* damage can result in extremely long reconstruction times. This
* will also test spilling from special to normal.
*/
if (psize >= metaslab_force_ganging && (random_in_range(100) < 3)) {
if (psize >= metaslab_force_ganging &&
metaslab_force_ganging_pct > 0 &&
(random_in_range(100) < MIN(metaslab_force_ganging_pct, 100))) {
metaslab_trace_add(zal, NULL, NULL, psize, d, TRACE_FORCE_GANG,
allocator);
return (SET_ERROR(ENOSPC));
Expand Down Expand Up @@ -6266,7 +6273,10 @@ ZFS_MODULE_PARAM(zfs_metaslab, zfs_metaslab_, switch_threshold, INT, ZMOD_RW,
"Segment-based metaslab selection maximum buckets before switching");

ZFS_MODULE_PARAM(zfs_metaslab, metaslab_, force_ganging, U64, ZMOD_RW,
"Blocks larger than this size are forced to be gang blocks");
"Blocks larger than this size are sometimes forced to be gang blocks");

ZFS_MODULE_PARAM(zfs_metaslab, metaslab_, force_ganging_pct, UINT, ZMOD_RW,
"Percentage of large blocks that will be forced to be gang blocks");

ZFS_MODULE_PARAM(zfs_metaslab, metaslab_, df_max_search, UINT, ZMOD_RW,
"Max distance (bytes) to search forward before using size tree");
Expand Down
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