Re: [PATCH RFC 3/9] memory: Introduce log_sync_global() to memory listener

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> Some of the memory listener may want to do log synchronization without
> being able to specify a range of memory to sync but always globally.
> Such a memory listener should provide this new method instead of the
> log_sync() method.
> 
> Obviously we can also achieve similar thing when we put the global
> sync logic into a log_sync() handler. However that's not efficient
> enough because otherwise memory_global_dirty_log_sync() may do the
> global sync N times, where N is the number of flat views.
> 
> Make this new method be exclusive to log_sync().
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

OK, so I guess the idea here is that when you have a ring with dirty
pages on it, you just need to clear all outstanding things on the ring
whereever they came from.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  include/exec/memory.h | 12 ++++++++++++
>  memory.c              | 33 +++++++++++++++++++++++----------
>  2 files changed, 35 insertions(+), 10 deletions(-)
> 
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index e85b7de99a..c4427094bb 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -533,6 +533,18 @@ struct MemoryListener {
>       */
>      void (*log_sync)(MemoryListener *listener, MemoryRegionSection *section);
>  
> +    /**
> +     * @log_sync_global:
> +     *
> +     * This is the global version of @log_sync when the listener does
> +     * not have a way to synchronize the log with finer granularity.
> +     * When the listener registers with @log_sync_global defined, then
> +     * its @log_sync must be NULL.  Vice versa.
> +     *
> +     * @listener: The #MemoryListener.
> +     */
> +    void (*log_sync_global)(MemoryListener *listener);
> +
>      /**
>       * @log_clear:
>       *
> diff --git a/memory.c b/memory.c
> index aeaa8dcc9e..53828ba00c 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -2016,6 +2016,10 @@ void memory_region_set_dirty(MemoryRegion *mr, hwaddr addr,
>                                          memory_region_get_dirty_log_mask(mr));
>  }
>  
> +/*
> + * If memory region `mr' is NULL, do global sync.  Otherwise, sync
> + * dirty bitmap for the specified memory region.
> + */
>  static void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
>  {
>      MemoryListener *listener;
> @@ -2029,18 +2033,24 @@ static void memory_region_sync_dirty_bitmap(MemoryRegion *mr)
>       * address space once.
>       */
>      QTAILQ_FOREACH(listener, &memory_listeners, link) {
> -        if (!listener->log_sync) {
> -            continue;
> -        }
> -        as = listener->address_space;
> -        view = address_space_get_flatview(as);
> -        FOR_EACH_FLAT_RANGE(fr, view) {
> -            if (fr->dirty_log_mask && (!mr || fr->mr == mr)) {
> -                MemoryRegionSection mrs = section_from_flat_range(fr, view);
> -                listener->log_sync(listener, &mrs);
> +        if (listener->log_sync) {
> +            as = listener->address_space;
> +            view = address_space_get_flatview(as);
> +            FOR_EACH_FLAT_RANGE(fr, view) {
> +                if (fr->dirty_log_mask && (!mr || fr->mr == mr)) {
> +                    MemoryRegionSection mrs = section_from_flat_range(fr, view);
> +                    listener->log_sync(listener, &mrs);
> +                }
>              }
> +            flatview_unref(view);
> +        } else if (listener->log_sync_global) {
> +            /*
> +             * No matter whether MR is specified, what we can do here
> +             * is to do a global sync, because we are not capable to
> +             * sync in a finer granularity.
> +             */
> +            listener->log_sync_global(listener);
>          }
> -        flatview_unref(view);
>      }
>  }
>  
> @@ -2727,6 +2737,9 @@ void memory_listener_register(MemoryListener *listener, AddressSpace *as)
>  {
>      MemoryListener *other = NULL;
>  
> +    /* Only one of them can be defined for a listener */
> +    assert(!(listener->log_sync && listener->log_sync_global));
> +
>      listener->address_space = as;
>      if (QTAILQ_EMPTY(&memory_listeners)
>          || listener->priority >= QTAILQ_LAST(&memory_listeners)->priority) {
> -- 
> 2.24.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK