Re: [Qemu-devel] [PATCH 02/30] memory: use a new FlatView pointer on every topology update

[Anthony Liguori <anthony@codemonkey.ws>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> This is the first step towards converting as->current_map to
> RCU-style updates, where the FlatView updates run concurrently
> with uses of an old FlatView.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>

Regards,

Anthony Liguori

> ---
>  memory.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index 1f44cd1..319894e 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -276,6 +276,7 @@ static void flatview_destroy(FlatView *view)
>          memory_region_unref(view->ranges[i].mr);
>      }
>      g_free(view->ranges);
> +    g_free(view);
>  }
>  
>  static bool can_merge(FlatRange *r1, FlatRange *r2)
> @@ -512,17 +513,18 @@ static void render_memory_region(FlatView *view,
>  }
>  
>  /* Render a memory topology into a list of disjoint absolute ranges. */
> -static FlatView generate_memory_topology(MemoryRegion *mr)
> +static FlatView *generate_memory_topology(MemoryRegion *mr)
>  {
> -    FlatView view;
> +    FlatView *view;
>  
> -    flatview_init(&view);
> +    view = g_new(FlatView, 1);
> +    flatview_init(view);
>  
>      if (mr) {
> -        render_memory_region(&view, mr, int128_zero(),
> +        render_memory_region(view, mr, int128_zero(),
>                               addrrange_make(int128_zero(), int128_2_64()), false);
>      }
> -    flatview_simplify(&view);
> +    flatview_simplify(view);
>  
>      return view;
>  }
> @@ -610,8 +612,8 @@ static void address_space_update_ioeventfds(AddressSpace *as)
>  }
>  
>  static void address_space_update_topology_pass(AddressSpace *as,
> -                                               FlatView old_view,
> -                                               FlatView new_view,
> +                                               const FlatView *old_view,
> +                                               const FlatView *new_view,
>                                                 bool adding)
>  {
>      unsigned iold, inew;
> @@ -621,14 +623,14 @@ static void address_space_update_topology_pass(AddressSpace *as,
>       * Kill ranges in the old map, and instantiate ranges in the new map.
>       */
>      iold = inew = 0;
> -    while (iold < old_view.nr || inew < new_view.nr) {
> -        if (iold < old_view.nr) {
> -            frold = &old_view.ranges[iold];
> +    while (iold < old_view->nr || inew < new_view->nr) {
> +        if (iold < old_view->nr) {
> +            frold = &old_view->ranges[iold];
>          } else {
>              frold = NULL;
>          }
> -        if (inew < new_view.nr) {
> -            frnew = &new_view.ranges[inew];
> +        if (inew < new_view->nr) {
> +            frnew = &new_view->ranges[inew];
>          } else {
>              frnew = NULL;
>          }
> @@ -674,14 +676,14 @@ static void address_space_update_topology_pass(AddressSpace *as,
>  
>  static void address_space_update_topology(AddressSpace *as)
>  {
> -    FlatView old_view = *as->current_map;
> -    FlatView new_view = generate_memory_topology(as->root);
> +    FlatView *old_view = as->current_map;
> +    FlatView *new_view = generate_memory_topology(as->root);
>  
>      address_space_update_topology_pass(as, old_view, new_view, false);
>      address_space_update_topology_pass(as, old_view, new_view, true);
>  
> -    *as->current_map = new_view;
> -    flatview_destroy(&old_view);
> +    as->current_map = new_view;
> +    flatview_destroy(old_view);
>      address_space_update_ioeventfds(as);
>  }
>  
> -- 
> 1.8.1.4