Re: [Qemu-devel] [PATCH 6/6] Don't abort on memory allocation error

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

* Orit Wasserman (owasserm@redhat.com) wrote:
> It is better to fail migration in case of failure to
> allocate new cache item

Does this actually fail migration or just drop back to sending an uncompressed
page? (I think the latter, and that's an even better result).

> Signed-off-by: Orit Wasserman <owasserm@redhat.com>
> ---
>  arch_init.c                    |  4 +++-
>  include/migration/page_cache.h |  4 +++-
>  page_cache.c                   | 16 +++++++++++-----
>  3 files changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 806d096..0bfbc5a 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -284,7 +284,9 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
>  
>      if (!cache_is_cached(XBZRLE.cache, current_addr)) {
>          if (!last_stage) {
> -            cache_insert(XBZRLE.cache, current_addr, current_data);
> +            if (cache_insert(XBZRLE.cache, current_addr, current_data) == -1) {
> +                return -1;
> +            }
>          }
>          acct_info.xbzrle_cache_miss++;
>          return -1;
> diff --git a/include/migration/page_cache.h b/include/migration/page_cache.h
> index 87894fe..d156f0d 100644
> --- a/include/migration/page_cache.h
> +++ b/include/migration/page_cache.h
> @@ -60,11 +60,13 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr);
>   * cache_insert: insert the page into the cache. the page cache
>   * will dup the data on insert. the previous value will be overwritten
>   *
> + * Returns -1 on error
> + *
>   * @cache pointer to the PageCache struct
>   * @addr: page address
>   * @pdata: pointer to the page
>   */
> -void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata);
> +int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata);
>  
>  /**
>   * cache_resize: resize the page cache. In case of size reduction the extra
> diff --git a/page_cache.c b/page_cache.c
> index 62a53f8..69e8329 100644
> --- a/page_cache.c
> +++ b/page_cache.c
> @@ -150,7 +150,7 @@ uint8_t *get_cached_data(const PageCache *cache, uint64_t addr)
>      return cache_get_by_addr(cache, addr)->it_data;
>  }
>  
> -void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
> +int cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
>  {
>  
>      CacheItem *it = NULL;
> @@ -161,16 +161,22 @@ void cache_insert(PageCache *cache, uint64_t addr, uint8_t *pdata)
>      /* actual update of entry */
>      it = cache_get_by_addr(cache, addr);
>  
> -    /* free old cached data if any */
> -    g_free(it->it_data);
> -
> +    /* allocate page */
>      if (!it->it_data) {
>          cache->num_items++;
> +        it->it_data = g_try_malloc(cache->page_size);
> +        if (!it->it_data) {
> +            DPRINTF("Error allocating page\n");
> +            return -1;
> +        }

It feels like it would have been correct to do the num_items++ after the 
allocation test (although since the num_items doesn't seem to be used
anywhere that's not a show-stopper, but worth fixing sometime).

>      }
>  
> -    it->it_data = g_memdup(pdata, cache->page_size);
> +    memcpy(it->it_data, pdata, cache->page_size);
> +
>      it->it_age = ++cache->max_item_age;
>      it->it_addr = addr;
> +
> +    return 0;
>  }
>  
>  int64_t cache_resize(PageCache *cache, int64_t new_num_pages)
> -- 
> 1.8.3.1

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

Dave
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK