RE: [PATCH 08/10] xen/arm: introduce reserved_page_list

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Jan

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Tuesday, May 18, 2021 3:39 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx; julien@xxxxxxx
> Subject: Re: [PATCH 08/10] xen/arm: introduce reserved_page_list
> 
> On 18.05.2021 07:21, Penny Zheng wrote:
> > Since page_list under struct domain refers to linked pages as gueast
> > RAM allocated from heap, it should not include reserved pages of static
> memory.
> >
> > The number of PGC_reserved pages assigned to a domain is tracked in a
> > new 'reserved_pages' counter. Also introduce a new reserved_page_list
> > to link pages of static memory. Let page_to_list return
> > reserved_page_list, when flag is PGC_reserved.
> >
> > Later, when domain get destroyed or restarted, those new values will
> > help relinquish memory to proper place, not been given back to heap.
> >
> > Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> > ---
> >  xen/common/domain.c     | 1 +
> >  xen/common/page_alloc.c | 7 +++++--
> >  xen/include/xen/sched.h | 5 +++++
> >  3 files changed, 11 insertions(+), 2 deletions(-)
> 
> This contradicts the title's prefix: There's no Arm-specific change here at 
> all.
> But imo the title is correct, and the changes should be Arm-specific. There's
> no point having struct domain fields on e.g. x86 which aren't used there at 
> all.
> 

Yep, you're right.
I'll add ifdefs in the following changes.

> > --- a/xen/common/page_alloc.c
> > +++ b/xen/common/page_alloc.c
> > @@ -2410,7 +2410,7 @@ int assign_pages(
> >
> >          for ( i = 0; i < nr_pfns; i++ )
> >          {
> > -            ASSERT(!(pg[i].count_info & ~PGC_extra));
> > +            ASSERT(!(pg[i].count_info & ~(PGC_extra |
> > + PGC_reserved)));
> >              if ( pg[i].count_info & PGC_extra )
> >                  extra_pages++;
> >          }
> > @@ -2439,6 +2439,9 @@ int assign_pages(
> >          }
> >      }
> >
> > +    if ( pg[0].count_info & PGC_reserved )
> > +        d->reserved_pages += nr_pfns;
> 
> I guess this again will fail to build on x86.
> 
> > @@ -588,6 +590,9 @@ static inline struct page_list_head *page_to_list(
> >      if ( pg->count_info & PGC_extra )
> >          return &d->extra_page_list;
> >
> > +    if ( pg->count_info & PGC_reserved )
> > +        return &d->reserved_page_list;
> 
> Same here.
> 
> Jan

Thanks
Penny