Re: Minutes from Feb 21 LSE Call

Andrea Arcangeli
2003-02-25T21:07:23Z

On Tue, Feb 25, 2003 at 12:53:44PM -0800, Martin J. Bligh wrote:
> >> > the only solution is to do rmap lazily, i.e. to start building the rmap
> >> > during swapping by walking the pagetables, basically exactly like I
> >> > refill the lru with anonymous pages only after I start to need this
> >> > information recently in my 2.4 tree, so if you never need to pageout
> >> > heavily several giga of ram (like most of very high end numa servers),
> >> > you'll never waste a single cycle in locking or whatever other
> >> > worthless accounting overhead that hurts performance of all common
> >> > workloads
> >>
> >> Did you see the partially object-based rmap stuff? I think that does
> >> very close to what you want already.
> >
> > I don't see how it can optimize away the overhead but I didn't look at
> > it for long.
>
> Because you don't set up and tear down the rmap pte-chains for every
> fault in / delete of any page ... it just works off the vmas.

so basically it uses the rmap that we always had since at least 2.2 for
everything but anon mappings, right? this is what DaveM did a few years
back too. This makes lots of sense to me, so at least we avoid the
duplication of rmap information, even if it won't fix the anonymous page
overhead, but clearly it's much lower cost for everything but anonymous
pages.

Andrea