ZFS ARC being limited below what is defined in /boot/loader.conf

[Steve Polyack]

On 02/12/10 13:47, Artem Belevich wrote:
> On Fri, Feb 12, 2010 at 10:31 AM, Steve Polyack<korvus at comcast.net>  wrote:
>
>    
>> Has anyone had an issue with the ZFS ARC max being limited below what has
>> been defined in /boot/loader.conf?  I just upgraded the RAM in a
>> ZFS-equipped system and attempted to devote 4GB to the ARC cache by placing
>> the following in loader.conf:
>>   vfs.zfs.arc_max="4096M"
>>
>> However, after rebooting, querying the sysctl gives me this:
>> $ sysctl vfs.zfs.arc_max
>> vfs.zfs.arc_max: 1726489600
>>
>> or about 1.7GB, an odd number that I can't find any references to.  For
>> reference, I'm running 8-STABLE (as of Jan 19th) on an amd64 system with 8GB
>> of RAM.  The system was previously very stable with 4GB of RAM and a 512MB
>> arc_max.  I have not modified vm.kmem_size_max (defaults to ~330GB on amd64)
>> or any other ZFS tunables.  I'd also like to avoid syncing up to the current
>> 8-STABLE if at all possible.
>>
>> Thanks,
>> Steve Polyack
>>
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>>      
>
> Check your vm.kmem_size. Default setting is way too low. Set it to at
> least double of desired arc size.
>
> --Artem
I mentioned it briefly, but vm.kmem_size_max was left at the default for 
amd64.  At 330GB it is way above and beyond what will ever be allocated 
to ARC:
$ sysctl vm.kmem_size_max
vm.kmem_size_max: 329853485875