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

[Peter Xu]

On Mon, Jun 03, 2019 at 02:10:34PM +0800, Wei Yang wrote:
> On Mon, Jun 03, 2019 at 02:05:47PM +0800, Wei Yang wrote:
> >On Mon, Jun 03, 2019 at 01:40:13PM +0800, Peter Xu wrote:
> >>
> >>Ah I see, thanks for the pointer.  Then I would agree it's fine.
> >>
> >>I'm not an expert of TCG - I'm curious on why all those three dirty
> >>bitmaps need to be set at the very beginning.  IIUC at least the VGA
> >>bitmap should not require that (so IMHO we should be fine to have all
> >>zeros with VGA bitmap for ramblocks, and we only set them when the
> >>guest touches them).  Migration bitmap should be special somehow but I
> >>don't know much on TCG/TLB part I'd confess so I can't say.  In other
> >>words, if migration is the only one that requires this "all-1"
> >>initialization then IMHO we may consider to remove the other part
> >>rather than here in migration because that's what we'd better to be
> >>sure with.
> >
> >I am not sure about the background here, so I didn't make a change at this
> >place.
> >
> >>
> >>And even if you want to remove this, I still have two suggestions:
> >>
> >>(1) proper comment here above bmap on the above fact that although
> >>    bmap is not set here but it's actually set somewhere else because
> >>    we'll sooner or later copy all 1s from the ramblock bitmap
> >>
> >>(2) imho you can move "migration_dirty_pages = 0" into
> >>    ram_list_init_bitmaps() too to let them be together
> >>
> 
> I took a look into this one.
> 
> ram_list_init_bitmaps() setup bitmap for each RAMBlock, while ram_state_init()
> setup RAMState. Since migration_dirty_pages belongs to RAMState, it maybe more
> proper to leave it at the original place.
> 
> Do you feel good about this?

Yes it's ok to me.  Thanks,

-- 
Peter Xu