Re: [Qemu-devel] [PATCH 06/10] migration: Make sure that we pass the right cache size

[Peter Xu <peterx@redhat.com>]

On Tue, Oct 10, 2017 at 08:15:38PM +0200, Juan Quintela wrote:
> Instead of passing silently round down the number of pages, make it an
> error that the cache size is not a multiple of 2.

s/multiple/power/?

Would this patch break existing users?

> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/page_cache.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/migration/page_cache.c b/migration/page_cache.c
> index 9a9d13d6a2..96268c3aea 100644
> --- a/migration/page_cache.c
> +++ b/migration/page_cache.c
> @@ -58,6 +58,13 @@ PageCache *cache_init(int64_t new_size, size_t page_size, Error **errp)
>          return NULL;
>      }
>  
> +    /* round down to the nearest power of 2 */
> +    if (!is_power_of_2(num_pages)) {
> +        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "cache size",
> +                   "is not a power of two number of pages");
> +        return NULL;
> +    }
> +
>      /* We prefer not to abort if there is no memory */
>      cache = g_try_malloc(sizeof(*cache));
>      if (!cache) {
> @@ -65,11 +72,6 @@ PageCache *cache_init(int64_t new_size, size_t page_size, Error **errp)
>                     "Failed to allocate cache");
>          return NULL;
>      }
> -    /* round down to the nearest power of 2 */
> -    if (!is_power_of_2(num_pages)) {
> -        num_pages = pow2floor(num_pages);
> -        DPRINTF("rounding down to %" PRId64 "\n", num_pages);
> -    }
>      cache->page_size = page_size;
>      cache->num_items = 0;
>      cache->max_num_items = num_pages;
> -- 
> 2.13.6
> 

-- 
Peter Xu