vm.kmem_size settings doesn't affect loader?

Ben Kelly bkelly at vadev.org
Fri Sep 26 16:13:54 UTC 2008

On Sep 26, 2008, at 4:43 AM, Bartosz Stec wrote:
> Jeremy Chadwick wrote:
>> These are the tuning settings I use:
>> vm.kmem_size="1536M"
>> vm.kmem_size_max="1536M"
>> vfs.zfs.arc_min="16M"
>> vfs.zfs.arc_max="64M"
> Yesterday I've added 512 MB memory to box (sum 1,5GB), and set  
> vm.kmem_size and vm.kmem_size to "1024M". With pieces of 1024MB,  
> 512MB, 256MB, 256MB available and 3 memory slots it is hard to have  
> 2GB RAM ;)
> Until now it survived world cleaning/building/installing/bonnie++  
> benchmarkink/fs scrubing and general usage. Memory usage seems  
> stable. If unfortunately kmem exhaustion will happen again I will  
> experiment with ARC settings.
> IMHO you've explained gently a lot of zfs tuning concerns in this  
> thread and they should be added to tuning guide - espacially  
> explanation of ARC and prefetch settings. Thanks again!

Did you increase KVA_PAGES in your kernel config as well?

The default of 256 only allows 1GB of kernel memory total.  Setting  
KVA_PAGES to 384 would probably be good for a kmem_size of 1GB.  This  
would give leave you with 512MB of space for other things in the  
kernel.  In your kernel config:

    options    KVA_PAGES=384

Sorry if you already knew this.  I know its in the zfs tuning guide.   
I just hadn't seen it mentioned in the thread yet and wanted to make  
sure it wasn't missed.

Hope that helps.

- Ben

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