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

[Peter Xu <peterx@redhat.com>]

On Mon, Jun 03, 2019 at 09:33:05AM +0800, Wei Yang wrote:
> On Sat, Jun 01, 2019 at 11:34:41AM +0800, Peter Xu wrote:
> >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:
> >
> 
> I have done some migration cases, like migrate a linux guest through tcp.

When did you start the migration?  Have you tried to migrate during
some workload?

> 
> Other cases suggested to do?

Could you also help answer the question I raised below in the link?

Thanks,

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

-- 
Peter Xu