RE: [Xen-devel] Regarding page table management changes from Xen v1to Xen v2 (and v3)

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> Although, same results can be obtained by doing the v1.2 way, 
> i.e. making one hypercall requesting these 1024 changes, no?

No, not easily -- the batched interface has problems with SMP guests, as
the updates may be expected to be individually atomic.

Ian

> On Wed, Apr 26, 2006 at 05:18:28PM +0100, Keir Fraser wrote:
> > 
> > On 26 Apr 2006, at 16:35, Himanshu Raj wrote:
> > 
> > >I am trying to understand the rationale behind this change. In 
> > >previous case, there would be no page faults due to page table 
> > >updates and only one hypercall.
> > >In the second case, there would be atleast 2 page faults due to PT 
> > >management activity, but no hypercalls. Besides, mapping and 
> > >remapping with different permissions imply removing this 
> entry from 
> > >TLB (which is hopefully being done with invlpg).
> > >Benefit of latter approach only seems to be the removal of xen 
> > >specific linux code. Why was the approach changed? Could someone 
> > >please shed some light on this?
> > 
> > It's useful for batched updates (e.g., fork()) where the 2 
> faults are 
> > amortised across up to 1024 pte changes.
> > 
> >  -- Keir
> 
> --
> --------------------------------------------------------------
> -----------
> Himanshu Raj
> PhD Student, GaTech (www.cc.gatech.edu/~rhim) I prefer to 
> receive attachments in an open, non-proprietary format.
> --------------------------------------------------------------
> -----------
> 
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