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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> --- 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