Re: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

[Michael S. Tsirkin]

On Thu, Apr 05, 2018 at 02:05:03AM +0000, Wang, Wei W wrote:
> On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> > On Thu, Apr 05, 2018 at 12:30:27AM +0000, Wang, Wei W wrote:
> > > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > > I'm afraid the driver couldn't be aware if the added hints are stale
> > > or not,
> > 
> > 
> > No - I mean that driver has code that compares two values and stops
> > reporting. Can one of the values be stale?
> 
> The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide if it needs to stop reporting hints, and cmd_id_received is what the driver reads from host (host notifies the driver to read for the latest value). If host sends a new cmd id, it will notify the guest to read again. I'm not sure how that could be a stale cmd id (or maybe I misunderstood your point here?)
> 
> Best,
> Wei

The comparison is done in one thread, the update in another one.

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MST