About Transparent Superpages and Non-transparent superapges

[Sebastian Kuzminsky]

On Sep 19, 2013, at 22:06 , Patrick Dung wrote:

> >We at Line Rate (now F5) are developing support for 1 Gig superpages on amd64.  We're basing our work on 9.1.0 for now.
> >
> >An early preview is available here:
> >
> >https://github.com/Seb-LineRate/freebsd/tree/freebsd-9.1.0-1gig-pages-NOT-READY-2
> 
> That is cool.
> 
> What type of applications can take advantage of the 1Gb page size?
> And is it transparent? Or applications need to be modified?

It's transparent for the kernel: all of UMA and kmem_malloc()/kmem_free() is backed by 1 gig superpages.

It's not transparent for userspace: applications need to pass a new flag to mmap() to get 1 gig pages.

This is useful in applications with high memory pressure, where memory bandwidth and TLB misses are a limiting factor.


-- 
Sebastian Kuzminsky