Re: [PATCH-for-5.2] memory: Display bigger regions first in 'info mtree' output

[Peter Xu]

On Mon, Jul 27, 2020 at 07:45:43PM +0200, Philippe Mathieu-Daudé wrote:
> When different regions have the same address, we currently
> sort them by the priority. Also sort them by the region
> size.
> 
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  softmmu/memory.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index af25987518..c28dcaf4d6 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -2960,7 +2960,8 @@ static void mtree_print_mr(const MemoryRegion *mr, 
> unsigned int level,
>          QTAILQ_FOREACH(ml, &submr_print_queue, mrqueue) {
>              if (new_ml->mr->addr < ml->mr->addr ||
>                  (new_ml->mr->addr == ml->mr->addr &&
> -                 new_ml->mr->priority > ml->mr->priority)) {
> +                 (MR_SIZE(new_ml->mr->size) > MR_SIZE(ml->mr->size) ||
> +                  new_ml->mr->priority > ml->mr->priority))) {
>                  QTAILQ_INSERT_BEFORE(ml, new_ml, mrqueue);
>                  new_ml = NULL;
>                  break;

Note that this change could make the outcome unpredictable... Assuming two
memory regions:

  mr1: addr=0, size=0x1000, pri=2
  mr2: addr=0, size=0x2000, pri=1

Then assuming submr_print_queue only contains these two mrs.  Then when
submr_print_queue has mr1 at head, then when we insert mr2 we'll think it
should be inserted before mr1 (because mr2's size bigger), so the result will 
be:

  mr2:...
  mr1:...

If submr_print_queue has mr2 at head, then when we insert mr1 we'll think it
should be inserted before mr2 (because mr1's priority higher).  We'll instead
get:

  mr1:...
  mr2:...

Phil, could I ask what's the case to be fixed?

-- 
Peter Xu