Re: [Qemu-devel] [PATCH] migratioin/ram: leave RAMBlock->bmap blank on allocating

[Peter Xu <peterx@redhat.com>]

On Fri, May 31, 2019 at 05:43:37PM +0100, Dr. David Alan Gilbert wrote:
> * Wei Yang (richardw.yang@linux.intel.com) wrote:
> > During migration, we would sync bitmap from ram_list.dirty_memory to
> > RAMBlock.bmap in cpu_physical_memory_sync_dirty_bitmap().
> > 
> > Since we set RAMBlock.bmap and ram_list.dirty_memory both to all 1, this
> > means at the first round this sync is meaningless and is a duplicated
> > work.
> > 
> > Leaving RAMBlock->bmap blank on allocating would have a side effect on
> > migration_dirty_pages, since it is calculated from the result of
> > cpu_physical_memory_sync_dirty_bitmap(). To keep it right, we need to
> > set migration_dirty_pages to 0 in ram_state_init().
> > 
> > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> 
> I've looked at this for a while, and I think it's OK, so
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> Peter, Juan: Can you just see if there's arny reason this would be bad,
> but I think it's actually more sensible than what we have.

I really suspect it will work in all cases...  Wei, have you done any
test (or better, thorough tests) with this change?  My reasoning of
why we should need the bitmap all set is here:

https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg07361.html

Regards,

-- 
Peter Xu