Re: [patch 0/6] MMU Notifiers V6

Robin Holt
2008-02-08T23:36:46Z

On Fri, Feb 08, 2008 at 03:32:19PM -0800, Christoph Lameter wrote:
> On Fri, 8 Feb 2008, Andrew Morton 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.

Thanks,
Robin