Re: [PATCH] Physical Memory Management [0/1]

Peter Zijlstra
2009-05-14T17:10:08Z

On Thu, 2009-05-14 at 10:07 -0700, Andrew Morton wrote:
> On Thu, 14 May 2009 15:04:55 +0200
> Micha__ Nazarewicz <m.nazarewicz@samsung.com> wrote:
>
> > On Thu, 14 May 2009 14:05:02 +0200, Peter Zijlstra wrote:
> > > And who says your pre-allocated pool won't fragment with repeated PMM
> > > use?
> >
> > Yes, this is a good question. What's more, there's no good answer. ;)
> >
>
> We do have capability in page reclaim to deliberately free up
> physically contiguous pages (known as "lumpy reclaim").
>
> It would be interesting were someone to have a go at making that
> available to userspace: ask the kernel to give you 1MB of physically
> contiguous memory. There are reasons why this can fail, but migrating
> pages can be used to improve the success rate, and userspace can be
> careful to not go nuts using mlock(), etc.
>
> The returned memory would of course need to be protected from other
> reclaim/migration/etc activity.

I thought we already exposed this, its called hugetlbfs ;-)