Re: [patch 0/6] MMU Notifiers V6

Christoph Lameter
2008-02-08T23:41:35Z

On Fri, 8 Feb 2008, Robin Holt wrote:

> > > What about ib_umem_get()?
> >
> > Ok. It pins using an elevated refcount. Same as XPmem right now. With that
> > we effectively pin a page (page migration will fail) but we will
> > continually be reclaiming the page and may repeatedly try to move it. We
> > have issues with XPmem causing too many pages to be pinned and thus the
> > OOM getting into weird behavior modes (OOM or stop lru scanning due to
> > all_reclaimable set).
> >
> > An elevated refcount will also not be noticed by any of the schemes under
> > consideration to improve LRU scanning performance.
>
> Christoph, I am not sure what you are saying here. With v4 and later,
> I thought we were able to use the rmap invalidation to remove the ref
> count that XPMEM was holding and therefore be able to swapout. Did I miss
> something? I agree the existing XPMEM does pin. I hope we are not saying
> the XPMEM based upon these patches will not be able to swap/migrate.

Correct.

You missed the turn of the conversation to how ib_umem_get() works.
Currently it seems to pin the same way that the SLES10 XPmem works.