RE: [RFC/PATCH] pfn_valid() more generic : arch independent part[0/2]

From: Luck, Tony <tony.luck_at_intel.com>
Date: 2004-10-08 01:53:32
>The normal way to fix the above is just to have a bitmap array 
>to test - in your case a 1GB granularity would be sufficicent. That 
>takes < 1 word to implement for the example above ;-)

In the general case you need a bit for each granule (since that is the
unit that the kernel admits/denies the existence of memory).  But the
really sparse systems end up with a large bitmap.  SGI Altix uses 49
physical address bits, and a granule size of 16MB ... so we need 2^25
bits ... i.e. 4MBbytes.  While that's a drop in the ocean on a 4TB
machine, it still seems a pointless waste.

-Tony
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Received on Thu Oct 7 11:58:57 2004

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