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Convert zfs_mg_noalloc_threshold to a module parameter and document 

The parameter was added as illumos issue 4081 which was committed to
zfsonlinux in ac72fac3ea.  This patch
documents the parameter and allows for it to be set as a module parameter.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2483
This commit is contained in:
Tim Chase 2014-07-09 22:36:03 -05:00 committed by Brian Behlendorf
parent d586964141
commit f4a4046bd6
2 changed files with 30 additions and 0 deletions
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26
man/man5/zfs-module-parameters.5
View File

@ -729,6 +729,32 @@ Disable meta data compression
Use \fB1\fR for yes and \fB0\fR for no (default).
.RE
.sp
.ne 2
.na
\fBzfs_mg_noalloc_threshold\fR (int)
.ad
.RS 12n
Defines a threshold at which metaslab groups should be eligible for
allocations. The value is expressed as a percentage of free space
beyond which a metaslab group is always eligible for allocations.
If a metaslab group's free space is less than or equal to the
the threshold, the allocator will avoid allocating to that group
unless all groups in the pool have reached the threshold. Once all
groups have reached the threshold, all groups are allowed to accept
allocations. The default value of 0 disables the feature and causes
all metaslab groups to be eligible for allocations.
This parameter allows to deal with pools having heavily imbalanced
vdevs such as would be the case when a new vdev has been added.
Setting the threshold to a non-zero percentage will stop allocations
from being made to vdevs that aren't filled to the specified percentage
and allow lesser filled vdevs to acquire more allocations than they
otherwise would under the old \fBzfs_mg_alloc_failures\fR facility.
.sp
Default value: \fB0\fR.
.RE
.sp
.ne 2
.na

4
module/zfs/metaslab.c
View File

@ -2120,4 +2120,8 @@ MODULE_PARM_DESC(metaslab_debug_load, "load all metaslabs during pool import");
module_param(metaslab_debug_unload, int, 0644);
MODULE_PARM_DESC(metaslab_debug_unload,
"prevent metaslabs from being unloaded");
module_param(zfs_mg_noalloc_threshold, int, 0644);
MODULE_PARM_DESC(zfs_mg_noalloc_threshold,
"percentage of free space for metaslab group to allow allocation");
#endif /* _KERNEL && HAVE_SPL */