Re: [Qemu-devel] [PATCH 1/2] migration: bitmap_set is unnecessary as bitmap_new uses g_try_malloc0

[Wen Congyang <wency@cn.fujitsu.com>]

On 09/25/2015 05:31 PM, Denis V. Lunev wrote:
> On 09/25/2015 12:24 PM, Wen Congyang wrote:
>> On 09/25/2015 05:09 PM, Denis V. Lunev wrote:
>>> we can omit calling of bitmap_set in migration_bitmap_extend and
>>> ram_save_setup just after bitmap_new, which properly zeroes memory
>>> inside.
>> This patch is wrong. bitmap_set() is set all bits of the memory to 1,
>> not 0.
>>
> 
> OK, then I'll replace g_try_malloc0 with g_try_malloc in the next patch to avoid
> double memset

No, bitmap_new() is called in many places. Some caller needs zero memory, and
some caller doesn't need...

> 
>>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>>> CC: Igor Redko <redkoi@virtuozzo.com>
>>> CC: Anna Melekhova <annam@virtuozzo.com>
>>> CC: Juan Quintela <quintela@redhat.com>
>>> CC: Amit Shah <amit.shah@redhat.com>
>>> CC: Wen Congyang <wency@cn.fujitsu.com>
>>> ---
>>>   migration/ram.c | 2 --
>>>   1 file changed, 2 deletions(-)
>>>
>>> diff --git a/migration/ram.c b/migration/ram.c
>>> index 7f007e6..a712c68 100644
>>> --- a/migration/ram.c
>>> +++ b/migration/ram.c
>>> @@ -1081,7 +1081,6 @@ void migration_bitmap_extend(ram_addr_t old, ram_addr_t new)
>>>            */
>>>           qemu_mutex_lock(&migration_bitmap_mutex);
>>>           bitmap_copy(bitmap, old_bitmap, old);
>>> -        bitmap_set(bitmap, old, new - old);
>>>           atomic_rcu_set(&migration_bitmap, bitmap);
>>>           qemu_mutex_unlock(&migration_bitmap_mutex);
>>>           migration_dirty_pages += new - old;
>>> @@ -1146,7 +1145,6 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
>>>         ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
>>>       migration_bitmap = bitmap_new(ram_bitmap_pages);
>>> -    bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
>>>         /*
>>>        * Count the total number of pages used by ram blocks not including any
>>>
> 
> .
>