kmem_size / arc_max ratio

Dan Nelson dnelson at
Wed Feb 3 18:55:01 UTC 2010

In the last episode (Feb 03), Rolf Nielsen said:
> I recently installed more RAM in my computer; increased it from 4GB to
> 8GB.  Mainly to be able to use a larger arc for zfs.  Now my question is,
> how much memory does the kernel need apart from the arc?  I currently have
> kmem_size_max 512MB bigger than arc_max.  I haven't run into any problems
> so far.  I use my computer as desktop only, running WindowMaker and
> normally having xconsole, emiclock, firefox with 5+ tabs, thunderbird,
> amsn, sunbird, thunar, ktorrent and upto 5 or 6 xterms.
> My loader.conf looks like this:
> vfs.root.mountfrom="zfs:sysroot"
> vm.kmem_size_max=5G
> vm.kmem_size=5G
> vfs.zfs.arc_max=4608M
> vm.pmap.pg_ps_enabled=1
> zfs_load="YES"
> nvidia_load="YES"

vm.kmem_size_max should default to something like 300GB now, so you can
remove that line.  vm.pmap.pg_ps_enabled defaults to 1 nowadays, too.  I
have an 8GB system and use these settings:


	Dan Nelson
	dnelson at

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