Date: Fri, 05 Mar 2004 16:11:55 -0600 From: Jon Noack <noackjr@alumni.rice.edu> To: Vincent Poy <vince@oahu.WURLDLINK.NET> Cc: current@freebsd.org Subject: Re: -CURRENT kernel panic Message-ID: <4048FB2B.1020001@alumni.rice.edu> In-Reply-To: <20040305022226.T8264-100000@oahu.WURLDLINK.NET> References: <20040305022226.T8264-100000@oahu.WURLDLINK.NET>
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On 3/5/2004 6:23 AM, Vincent Poy wrote:
> On Fri, 5 Mar 2004, Jon Noack wrote:
>> On 3/4/2004 4:13 PM, Vincent Poy wrote:
>>> On Thu, 4 Mar 2004, Andrew Gallatin wrote:
>>>> Vincent Poy writes:
>>>>> Interesting. I'm still wondering what the VM_KMEM_SIZE_SCALE
>>>>> number represents.
>>>>
>>>> It tries to autoscale the kmem size, so that you don't need to hard
>>>> code it. Hardcoding it could be bad if you change the amount of ram
>>>> in the box.
>>>
>>> That part I understand but what exactly does the number 2 and 3
>>> mean?
>>
>> VM_KMEM_SIZE_SCALE:
>> How many physical pages per KVA page allocated.
>>
>> <snip>
>
> I actually read that part already but is 2 basically 1/2 and 3
> actually just 1/3?
That's the way I read it -- check out this comment again (from
src/sys/i386/include/vmparam.h -- hopefully the formatting will be ok):
> /*
> * How many physical pages per KVA page allocated.
> * min(max(VM_KMEM_SIZE, Physical memory/VM_KMEM_SIZE_SCALE),
VM_KMEM_SIZE_MAX)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> * is the total KVA space allocated for kmem_map.
> */
VM_KMEM_SIZE_SCALE is used to autoscale the value in this range:
VM_KMEM_SIZE <= vm_kmem_size <= VM_KMEM_SIZE_MAX
This ensures we have a reasonable minimum (VM_KMEM_SIZE) and maximum
(VM_KMEM_SIZE_MAX) while making a fair effort at efficiently utilizing
available memory (Physical memory/VM_KMEM_SIZE_SCALE).
Jon Noack
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