Re: [Linux-ia64] IA64 Linux Kernel Page Sizes

[Erich Focht <focht@ess.nec.de>]

Dear Rohit,

I'd like to try the super large pages which you mentioned in your mail. I
tried the 64k pages with IA64 Linux but the performance advantage was less
than expected (at least with the applications I used)...

Thanks a lot in advance!

Best regards,
Erich


---
Erich Focht                                    <efocht@ess.nec.de>
NEC European Supercomputer Systems, European HPC Technology Center


On Fri, 7 Sep 2001, Seth, Rohit wrote:

> I have an early prototype of super large page(256MB) implementation.  This
> is only a proof of concept for large apps (and configurations) to use super
> large pages.  The use is for apps that need large data regions (Instructions
> and regular data still use regular page size). Current implementation is
> through shared memory calls (shmat) with either SHM_LPAGE (a new flag) or
> size of requested segment >=LPAGE_SIZE(256MB).  In either case the size has
> to be multiple of LPAGE_SIZE to get a large shared memory segment.  Further
> the whole physical memory is divided in two parts, one that is seen by
> kernel and the other that is only used to fill in large page requests.  And
> there is no moving of memory between two parts (in case of shortages). This
> implementation is based on 2.4.5 kernel.  Currently IA-32 apps don't work in
> this environment, but that can be fixed.
> 
> Let me know if this fits in your requirements and you want to give this a
> try.  I can send you a cut of (modified)tar files out of my source tree
> early next week.
> 
> rohit
> 
> -----Original Message-----
> From: Donny Cooper [mailto:dcooper@atcc.necsys.com]
> Sent: Thursday, September 06, 2001 9:23 AM
> To: linux-ia64@linuxia64.org
> Cc: Cooper (E-mail)
> Subject: [Linux-ia64] IA64 Linux Kernel Page Sizes
> 
> 
> (1) Below is a previous mail, from David M., responding to page size
> questions for IA64 kernels.
> 
> > As for the future: I'd like to start playing with superpage support
> > fairly soon (once I get some spare time on my hands... ;-).  With
> > superpages, physically contiguous regions of memory could be mapped
> > with a single TLB entry, giving you most of the benefit of (very)
> > large page sizes.	--david
> 
> Are there any updates on these plans?
> 
> 
> (2) Below are current available kernel options (from config).
> 
> 4KB	For best IA-32 compatibility
> 8KB   For best IA-64 performance
> 16KB 	For best IA-64 performance
> 64KB	Not for Itanium.
> 
> What is "IA64 best performance" based on?
> 
> We have a large memory system (32GB), and are not concerned with wasting
> memory during certain benchmarks.  Are 64KB
> pages truly not functional on Itanium, or just not recommended because of
> memory waste.  To my knowledge, HP-UX seems to
> benefit from 64KB pages on ITANIUM.
> 
> Any input or recommendation on these items is appreciated.
> 
> 
> Thanks.
> -----------------------------------
> Donny Cooper
> NEC Systems, Inc.
> Advanced Technical Computing Center
> dcooper@atcc.necsys.com
> www.necservers.com
> -----------------------------------