Re: [Qemu-devel] [PATCH 1/2] memory: Replace has_coalesced_range with add/del flags

[Peter Xu <peterx@redhat.com>]

On Mon, Aug 19, 2019 at 04:30:45PM +0200, Paolo Bonzini wrote:
> On 17/08/19 11:32, Peter Xu wrote:
> > The previous has_coalesced_range counter has a problem in that it only
> > works for additions of coalesced mmio ranges but not deletions.  The
> > reason is that has_coalesced_range information can be lost when the
> > FlatView updates the topology again when the updated region is not
> > covering the coalesced regions. When that happens, due to
> > flatrange_equal() is not checking against has_coalesced_range, the new
> > FlatRange will be seen as the same one as the old and the new
> > instance (whose has_coalesced_range will be zero) will replace the old
> > instance (whose has_coalesced_range _could_ be non-zero).
> > 
> > To fix it, we don't cache has_coalesced_range at all in the FlatRange.
> > Instead we introduce two flags to make sure the coalesced_io_{add|del}
> > will only be called once for every FlatRange instance.  This will even
> > work if another FlatRange replaces current one.
> 
> It's still a bit ugly that coalesced_mmio_add_done ends up not being set
> on the new (but equal) FlatRange.
> 
> Would something like this work too?
> 
> diff --git a/memory.c b/memory.c
> index edd0c13..fc91f06 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -939,6 +939,7 @@ static void address_space_update_topology_pass(AddressSpace *as,
>              /* In both and unchanged (except logging may have changed) */
>  
>              if (adding) {
> +                frnew->has_coalesced_range = frold->has_coalesced_range;
>                  MEMORY_LISTENER_UPDATE_REGION(frnew, as, Forward, region_nop);
>                  if (frnew->dirty_log_mask & ~frold->dirty_log_mask) {
>                      MEMORY_LISTENER_UPDATE_REGION(frnew, as, Forward, log_start,

This seems to be a much better (and, shorter) idea. :-)

I'll verify it and repost if it goes well.

Regards,

-- 
Peter Xu