After few hours with dtrace and source code browsing I found that in my space
map there are no 128K blocks left.
Try this on your ZFS.
dtrace -n fbt::metaslab_group_alloc:return'/arg1 == -1/{}
If you will get probes, then you also have the same problem.
Allocating from space map works like this:
1. metaslab_group_alloc want to allocate 128K block size
2. for (all metaslabs) {
read space map and check 128K block size
if no block then remove flag METASLAB_ACTIVE_MASK
}
3. unload maps for all metaslabs without METASLAB_ACTIVE_MASK
Thats is why spa_sync take so much time.
Now the workaround:
zfs set recordsize=8K pool
Now the spa_sync functions takes 1-2 seconds, processor is idle,
only few metaslabs space maps are loaded:
> 00000600103ee500::walk metaslab |::print struct metaslab ms_map.sm_loaded !
> grep -c "0x"
3
But now I have another question.
How 8k blocks will impact on performance ?
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