Large-page support

Large-page support

[Santosh Abraham]

Hi,

What is the current level of large page support implemented
for Linux ?

Can applications specify a certain page-size to use for
their private mappings ? Is this limited to any particular page-size ?

Is smart-demotion implemented ?

thanks
santosh.

RE: Large-page support

[Luck, Tony]

>What is the current level of large page support implemented
>for Linux ?

Linux currently doesn't support "large" pages ... but it does support
"huge" ones.

On ia64 there is a kernel compile-time choice for the regular page size
between 4k, 8k, 16k and 64k.  The default is 16k.

Huge page size is selectable via a boot-time parameter "hugepagesz=",
choices are just about anything supported by h/w (current implementations
of Itanium 2 support even powers of two up to 4G). Default is 256MB.

>Can applications specify a certain page-size to use for
>their private mappings ? Is this limited to any particular page-size ?

No ... normal allocations are done using the default system page
size.  To see how to use huge pages, read Documentation/vm/hugetlbpage.txt
in the Linux kernel sources.

>Is smart-demotion implemented ?
No.

-Tony

RE: Large-page support

[Santosh Abraham]

Thanks for the info !

If I read it correctly the flags need to be
MAP_FIXED|MAP_SHARED ? No support for MAP_PRIVATE ?

Any good reading available on why we need
a hugetlbfs ? 

TIA,
-santosh.



> -----Original Message-----
> From: Luck, Tony [mailto:tony.luck@intel.com] 
> Sent: Tuesday, August 23, 2005 9:55 PM
> To: santosh.abraham@hp.com; linux-ia64@vger.kernel.org
> Subject: RE: Large-page support
> 
> 
> >What is the current level of large page support implemented 
> for Linux ?
> 
> Linux currently doesn't support "large" pages ... but it does 
> support "huge" ones.
> 
> On ia64 there is a kernel compile-time choice for the regular 
> page size between 4k, 8k, 16k and 64k.  The default is 16k.
> 
> Huge page size is selectable via a boot-time parameter 
> "hugepagesz=", choices are just about anything supported by 
> h/w (current implementations of Itanium 2 support even powers 
> of two up to 4G). Default is 256MB.
> 
> >Can applications specify a certain page-size to use for
> >their private mappings ? Is this limited to any particular 
> page-size ?
> 
> No ... normal allocations are done using the default system 
> page size.  To see how to use huge pages, read 
> Documentation/vm/hugetlbpage.txt in the Linux kernel sources.
> 
> >Is smart-demotion implemented ?
> No.
> 
> -Tony
> 
> 

Re: Large-page support

[Grant Grundler]

On Wed, Aug 24, 2005 at 09:54:41AM +0530, Santosh Abraham wrote:
> Any good reading available on why we need
> a hugetlbfs ? 

Yes. Googling got me here:
	http://developer.osdl.org/maryedie/LWE_NYC04_Links.html

See the top couple of links.

You might also read about superpages to get some of the background:
	http://lwn.net/Articles/40840/

grant