Re: [Xen-devel] [RFC PATCH] PVH: cleanup of p2m upon p2m destroy

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Tue, 17 Dec 2013 08:42:32 +0000
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> >>> On 17.12.13 at 02:47, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> >>> wrote:
> > When a controlling domain is destroyed, any p2m_is_foreign pages
> > must release the refcnt gotten when the page was added to the p2m.
> > 
> > Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
> 
> First of all, you leave open what the relationship of this is with
> your 7-patch v7 series. Why is this not part of it? Obviously any
> necessary cleanup would logically have to come no later than
> where the first creation of pages of this type happens...

I was intending this for 4.5, and the series for 4.4, but now i can
combine it since the series is out of 4.4.


> > +/* This function to do any cleanup while walking the entire p2m */
> > +int p2m_cleanup(struct domain *d)
> > +{
> > +    int rc = 0;
> > +    unsigned long gfn, count = 0;
> > +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
> > +
> > +    if ( !is_pvh_domain(d) )
> > +        return 0;
> > +
> > +    for ( gfn = p2m->next_foreign_gfn_to_check;
> > +          gfn <= p2m->max_mapped_pfn; gfn++, count++ )
> > +    {
> > +        p2m_type_t p2mt;
> > +        mfn_t mfn = get_gfn_query(d, gfn, &p2mt);
> > +
> > +        if ( unlikely(p2m_is_foreign(p2mt)) )
> > +            put_page(mfn_to_page(mfn));
> > +        put_gfn(d, gfn);
> > +        
> > +        /* Preempt every 10k pages, arbritary */
> > +        if ( count == 10000 && hypercall_preempt_check() )
> > +        {
> > +            p2m->next_foreign_gfn_to_check = gfn + 1;
> > +            rc = -EAGAIN;
> > +            break;
> > +        }
> 
> So it looks like you copied one of the two obvious bugs from
> relinquish_shared_pages() _and_ deferred the preemption point

LOL...

> by quite a bit - 10,000 pages is quite a lot, the 512 used there
> seems much more reasonable.

Because the foreign pages are very small amount, so the loop is
mostly not doing anything. ok, will reduce it to 1k.

thanks
Mukesh


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