Re: hugepage patches

["Martin J. Bligh" <mbligh@aracnet.com>]

>> > O.k.  Then the code definitely needs to handle shared mappings..
>> 
>> Why? we just divided the pagetable size by a factor of 1000, so
>> the problem is no longer really there ;-)
> 
> William said one of the cases was to handle massively shared
> mappings.  You cannot create a massively shared mapping except by
> sharing.
> 
> Did I misunderstand what was meant by a massively shared mapping?
> 
> I can't imagine it being useful to guys like oracle without MAP_SHARED
> support....

Create a huge shmem segment. and don't share the pagetables. Without large
pages, it's an enormous waste of space in mindless duplication. With large
pages, it's a much smaller waste of space (no PTEs) in mindless
duplication. 
Still not optimal, but makes the problem manageable.

> Cool.  I have no doubt the benefit is there.    Measuring how large it
> is will certainly be interesting.

See the IBM research group's paper on large page support from last years
OLS. Pretty impressive stuff.

M.


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