[Beowulf] Feedback on large pages in Linux

Toon Moene toon at moene.indiv.nluug.nl
Mon Jul 17 16:48:24 EDT 2006


Joe Landman wrote:

> Toon Moene wrote:
> 
>>> 6. What would make large page support in Linux better for your 
>>> application?
>>
>> Duh. Fewer TLB cache reloads.
> 
> I would think that a simpler mechanism (not the "filesystem" approach) 
> would be better.  I would like to simply let an application use large 
> pages for its allocations.  Used to do this with IRIX and it was great.

Fascinating.

How would you envision this done ?

Most of our "large memory usage" is of the form:

main program:

       READ * L, M, N
       CALL MAIN(L, M, N)
       ...
       END
....
separate file:
       SUBROUTINE MAIN(L, M, N)
       REAL U(L, M, N), V(L, M, N), T(L, M, N), Q(L, M, N)
       ....
etc.

I.e., the memory used (automatic arrays) is based on the stack (at 
least, that's how most Fortran compilers would implement it.

The "application" doesn't allocate these pages, the operating system does.

Cheers,

-- 
Toon Moene - e-mail: toon at moene.indiv.nluug.nl - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
A maintainer of GNU Fortran 95: http://gcc.gnu.org/fortran/
Gfortran At Work: http://mysite.verizon.net/serveall/moene.pdf
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