Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

Andrea Arcangeli
2008-02-09T01:57:17Z

On Fri, Feb 08, 2008 at 05:27:03PM -0800, Christoph Lameter wrote:
> Pages will still be on the LRU and cycle through rmap again and again.
> If page migration is used on those pages then the code may make repeated
> attempt to migrate the page thinking that the page count must at some
> point drop.
>
> I do not think that the page count was intended to be used to pin pages
> permanently. If we had a marker on such pages then we could take them off
> the LRU and not try to migrate them.

The VM shouldn't break if try_to_unmap doesn't actually make the page
freeable for whatever reason. Permanent pins shouldn't happen anyway,
so defining an ad-hoc API for that doesn't sound too appealing. Not
sure if old hardware deserves those special lru-size-reduction
optimizations but it's not my call (certainly swapoff/mlock would get
higher priority in that lru-size-reduction area).