Re: [Qemu-devel] [PATCH] migratioin/ram: leave RAMBlock->bmap blank on allocating

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

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> During migration, we would sync bitmap from ram_list.dirty_memory to
> RAMBlock.bmap in cpu_physical_memory_sync_dirty_bitmap().
> 
> Since we set RAMBlock.bmap and ram_list.dirty_memory both to all 1, this
> means at the first round this sync is meaningless and is a duplicated
> work.
> 
> Leaving RAMBlock->bmap blank on allocating would have a side effect on
> migration_dirty_pages, since it is calculated from the result of
> cpu_physical_memory_sync_dirty_bitmap(). To keep it right, we need to
> set migration_dirty_pages to 0 in ram_state_init().
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>

I've looked at this for a while, and I think it's OK, so

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

Peter, Juan: Can you just see if there's arny reason this would be bad,
but I think it's actually more sensible than what we have.

Dave
> ---
>  migration/ram.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 95c51109d2..417874707d 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -3151,12 +3151,7 @@ static int ram_state_init(RAMState **rsp)
>      qemu_mutex_init(&(*rsp)->src_page_req_mutex);
>      QSIMPLEQ_INIT(&(*rsp)->src_page_requests);
>  
> -    /*
> -     * Count the total number of pages used by ram blocks not including any
> -     * gaps due to alignment or unplugs.
> -     */
> -    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
> -
> +    (*rsp)->migration_dirty_pages = 0;
>      ram_state_reset(*rsp);
>  
>      return 0;
> @@ -3172,7 +3167,6 @@ static void ram_list_init_bitmaps(void)
>          RAMBLOCK_FOREACH_NOT_IGNORED(block) {
>              pages = block->max_length >> TARGET_PAGE_BITS;
>              block->bmap = bitmap_new(pages);
> -            bitmap_set(block->bmap, 0, pages);
>              if (migrate_postcopy_ram()) {
>                  block->unsentmap = bitmap_new(pages);
>                  bitmap_set(block->unsentmap, 0, pages);
> -- 
> 2.19.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK