Re: objrmap and vmtruncate

[Martin J. Bligh]

> It also makes it easy to calculate the overhead of the pte chains: twice
> the amount of pagetable overhead. Ie. with 32-bit pte's it's +8 bytes
> overhead, or +0.2% of RAM overhead per mapped page, using a 4K page. With
> 64-bit ptes on 32-bit platforms (PAE), the overhead is still 8 bytes. On
> 64-bit platforms using 8K pages the overhead is still +0.2% of RAM, in
> additionl to the 0.1% of RAM overhead for the pte itself. The worst-case
> is 64-bit platforms with a 4K pagesize, there the overhead is +0.4% of
> RAM, in addition to the 0.2% overhead caused by the pte itself.

Oh, BTW. You're assuming no sharing of any pages in the above. Look what
happens if 1000 processes share the same page ... 

M.