Yang Hongyang <yanghongy...@huawei.com> wrote:
> Hi Juan,
>
> On 2017/3/24 16:29, Juan Quintela wrote:
>> Yang Hongyang <yanghongy...@huawei.com> wrote:
>>> On 2017/3/24 4:45, Juan Quintela wrote:
>>>> We change the meaning of start to be the offset from the beggining of
>>>> the block.
>>>>
>>>> @@ -701,7 +701,7 @@ static void migration_bitmap_sync(RAMState *rs)
>>>> qemu_mutex_lock(&rs->bitmap_mutex);
>>>> rcu_read_lock();
>>>> QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
>>>> - migration_bitmap_sync_range(rs, block->offset,
>>>> block->used_length);
>>>> + migration_bitmap_sync_range(rs, block, 0, block->used_length);
>>>
>>> Since RAMBlock been passed to bitmap_sync, could we remove
>>> param 'block->used_length' either?
>>
>> Hi
>>
>> good catch.
>>
>> I had that removed, and then realized that I want to synchronize parts
>> of the bitmap, not the whole one. That part of the series is still not
>> done.
>>
>> Right now we do something like (I have simplified a lot of details):
>>
>> while(true) {
>> foreach(block)
>> bitmap_sync(block)
>> foreach(page)
>> if(dirty(page))
>> page_send(page)
>> }
>>
>>
>> If you have several terabytes of RAM that is too ineficient, because
>> when we arrive to the page_send(page), it is possible that it is already
>> dirty again, and we have to send it twice. So, the idea is to change to
>> something like:
>>
>> while(true) {
>> foreach(block)
>> bitmap_sync(block)
>
> Do you mean sync with KVM here?
>
>> foreach(block)
>> foreach(64pages)
>> bitmap_sync(64pages)
>
> Then here, we will sync with KVM too. For huge MEM,
> it will generates lots of ioctl()...
> Bitmap in KVM is per Memory region IIRC. KVM module currently
> haven't the ability to sync parts of the bitmap. A sync have
> to sync the whole mr. So if we want to do small sync, we might
> need to modify KVM also, but that still won't solve the preblem
> of increased ioctls.
And why I remembered incorrectly that we could sync part of the bitmaps.
Yes, we could have more ioctls, but less pages written twice, it is a
tradeoff, at some point it makes sense to change it.
Problem is that now this is going to be more difficult that I thought to
test for it.
Thanks, Juan.
