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

Seth, Rohit
2001-09-07T17:01:08Z

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
-----------------------------------

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