Re: [Qemu-devel] [PATCH 2/2] migration/xbzrle: cleanup the handling cache miss condition

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

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> For cache miss condition not in last_stage, we need to insert data into
> cache. When this step succeed, current_data should be updated. While no
> matter these checks pass or not, -1 is returned.
> 
> Based on this, the logic in cache miss handling could be simplified a
> little.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  migration/ram.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 878cd8de7a..67ba075cc4 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1572,15 +1572,14 @@ static int save_xbzrle_page(RAMState *rs, uint8_t **current_data,
>      if (!cache_is_cached(XBZRLE.cache, current_addr,
>                           ram_counters.dirty_sync_count)) {
>          xbzrle_counters.cache_miss++;
> -        if (!last_stage) {
> -            if (cache_insert(XBZRLE.cache, current_addr, *current_data,
> -                             ram_counters.dirty_sync_count) == -1) {
> -                return -1;
> -            } else {
> -                /* update *current_data when the page has been
> -                   inserted into cache */
> -                *current_data = get_cached_data(XBZRLE.cache, current_addr);
> -            }
> +        if (!last_stage &&
> +            !cache_insert(XBZRLE.cache, current_addr, *current_data,
> +                          ram_counters.dirty_sync_count)) {
> +            /*
> +             * update *current_data when the page has been inserted into
> +             * cache
> +             */
> +            *current_data = get_cached_data(XBZRLE.cache, current_addr);

No this change doesn't gain anything and I find the original easier to
read.

This function is really subtle, every time I do anything with it I have
to think really hard about it, so ease of reading is more important.

Dave

>          }
>          return -1;
>      }
> -- 
> 2.19.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK