Re: [RFC] Track mlock()ed pages

Andrew Morton
2007-01-26T18:10:36Z

On Fri, 26 Jan 2007 07:44:42 -0800 (PST)
Christoph Lameter <clameter@sgi.com> wrote:

> On Fri, 26 Jan 2007, Andrew Morton wrote:
>
> > > > > Track mlocked pages via a ZVC
> >
> > Why?
>
> Large amounts of mlocked pages may be a problem for
>
> 1. Reclaim behavior.
>
> 2. Defragmentation
>

We know that. What has that to do with this patch?

>
> > You could perhaps go for a walk across all the other vmas which presently
> > map this page. If any of them have VM_LOCKED, don't increment the counter.
> > Similar on removal: only decrement the counter when the final mlocked VMA
> > is dropping the pte.
>
> For that we would need an additional refcount for vmlocked maps in the
> page struct.

No you don't. The refcount is already there. It is "the sum of the VM_LOCKED
VMAs which map this page".

It might be impractical or expensive to calculate it, but it's there.