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

[Orit Wasserman <owasserm@redhat.com>]

On 01/30/2014 06:08 PM, Dr. David Alan Gilbert wrote:
> * 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).
>

It fails the migration, if the users wants to disable compression it can do it
and start migration again.

>> 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).
>

You are correct, I will move it after allocation.

Orit
>>       }
>>
>> -    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
>