[Bug 224080] ZFS: "arc_dnlc_evicts_thr" + "arc_reclaim_thread" - high CPU load during poudriere build...

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=224080

--- Comment #29 from Cy Schubert <cy at FreeBSD.org> ---
(In reply to Jeff Roberson from comment #26)
I've applied a patch similar to the one discussed here. There is some
improvement but more testing and comparison with r326347 removed is needed.

On my two 8 GB machines (with zfs arc tuning removed from loader.conf) I get:

2 core + 2 threads:
CPU:  0.9% user, 95.9% nice,  3.0% system,  0.0% interrupt,  0.2% idle
Mem: 1500M Active, 318M Inact, 33M Laundry, 1762M Wired, 154M Buf, 4148M Free
ARC: 840M Total, 141M MFU, 545M MRU, 16M Anon, 12M Header, 127M Other
     288M Compressed, 893M Uncompressed, 3.10:1 Ratio

slippy# sysctl vm.kmem_size
vm.kmem_size: 8138756096
slippy# sysctl vm.kmem_size_max
vm.kmem_size_max: 1319413950874
slippy# sysctl hw.physmem
hw.physmem: 8365903872
slippy# 
slippy$ sysctl vfs.zfs.arc_max  
vfs.zfs.arc_max: 7065014272
slippy$ 

2 core:
CPU:  0.0% user, 94.9% nice,  4.1% system,  0.6% interrupt,  0.4% idle
Mem: 752M Active, 269M Inact, 1705M Wired, 111M Buf, 5215M Free
ARC: 862M Total, 218M MFU, 456M MRU, 15M Anon, 15M Header, 156M Other
     343M Compressed, 1079M Uncompressed, 3.15:1 Ratio


cwsys# sysctl vm.kmem_size
vm.kmem_size: 8325849088
cwsys# sysctl vm.kmem_size_max
vm.kmem_size_max: 1319413950874
cwsys# sysctl hw.physmem
hw.physmem: 8566394880
cwsys# 
cwsys$ sysctl vfs.zfs.arc_max  
vfs.zfs.arc_max: 7252107264
cwsys$ 

It appears arc is being limited to ~ 840 - 860 MB on the 8 GB machines.

The 5 GB machine (2 core):
CPU:  0.0% user, 95.1% nice,  4.7% system,  0.2% interrupt,  0.0% idle
Mem: 590M Active, 147M Inact, 1126M Wired, 101M Buf, 3077M Free
ARC: 488M Total, 50M MFU, 334M MRU, 6630K Anon, 5713K Header, 91M Other
     107M Compressed, 431M Uncompressed, 4.02:1 Ratio

bob# sysctl vm.kmem_size
vm.kmem_size: 5180735488
bob# sysctl vm.kmem_size_max
vm.kmem_size_max: 1319413950874
bob# sysctl hw.physmem
hw.physmem: 5345284096
bob# 
bob# sysctl vfs.zfs.arc_max  
vfs.zfs.arc_max: 4106993664
bob# 


We might want to consider reverting r326347 until we can fix this.

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