RE: Re: mem-event interface

[Dan Magenheimer <dan.magenheimer@oracle.com>]

> From: Patrick Colp [mailto:pjcolp@cs.ubc.ca]
> Sent: Sunday, June 27, 2010 11:40 AM
> To: Grzegorz Milos
> Cc: Xen-Devel (E-mail); Tim Deegan; George Dunlap; Bryan D. Payne;
> Andrew Peace; Steven Hand
> Subject: Re: [Xen-devel] Re: mem-event interface
> 
> On 27 June 2010 08:45, Grzegorz Milos <grzegorz.milos@gmail.com> wrote:
> >> I agree that multiple rings are a good idea here - especially if we
> want
> >> to disaggregate and have event handlers in multiple domains.
> >>
> >> Maybe the ring-registering interface could take a type and a
> rangeset -
> >> that would reduce the amount of extra chatter at the cost of some
> more
> >> overhead in Xen.
> >>
> >
> > Well, the trouble is what do units you express the ranges in. In pfns
> > belonging to a given guest, or in mfns? Either way memory sharing
> > would use <0 - max_{p,m}fn> rangeset most of the time. Similarly for
> > teh pager (I believe). Bryan, could you comment on XenAccess? I guess
> > rangesets would be useful there the most.
> >
> > I certainly agree that we will have to swallow some complexity in
> Xen,
> > to make the interface efficient. Some filters will have to live in
> > Xen, in order not to generate unnecessarily large rate of no-op
> > events.
> 
> I suppose one way to handle the range is to specify the range in terms
> of full address (i.e. not pfn, so page 0xf would be specified as
> 0xf000). This way, we can specify the full range of memory (e.g.
> <0xf000, 0xf001> to watch the first byte of the page with pfn 0xf).
> However, it might be useful to have a flag that lets you specify if
> you mean pfns, mfns, or full address ranges (or something of the
> like). Xen should return some sort of unique identifier for each
> handler so that new ranges can easily be added/removed dynamically.

Probably a good idea to plan for page sizes different from 4K anyway.
I wouldn't be surprised if a 2M-pagesize-only Xen exists in the
not-too-distant future.