XFS memory recomendation?

[Stan Hoeppner]

On 2/16/2012 8:49 PM, Dave Chinner wrote:
> On Thu, Feb 16, 2012 at 12:50:57PM +0100, Assarsson, Emil wrote:
>> Hi,
>>
>> Are there any recommendations about how much memory I need based
>> on the size of the file system and/or amount of files?  For
>> example: how much memory would be optimal for a 20TB file system
>> with 3000000 files? 
> 
> /me shrugs
> 
>> I guess it depends on the usage pattern?
> 
> Totally.

Allow me to drag the OP's question under a different light...

I have a 20TB XFS filesystem with 3000000 files.  What is the minimum
amount of system RAM I will need to run an xfs_check or xfs_repair or
xfs_[tool] on this filesystem, assuming Linux has been put into a low
overhead state, and said tool[s] has access to the bulk of the system
memory?

Is there a formula available so any XFS user can calculate this
xfs_[tools] RAM requirement, given FS size X and file count Y?

-- 
Stan