Re: [PATCH v8 1/5] mm: introduce a common interface for balloonpages mobility

[Rafael Aquini]

On Thu, Aug 23, 2012 at 07:25:05PM +0300, Michael S. Tsirkin wrote:
> On Thu, Aug 23, 2012 at 04:53:28PM +0300, Michael S. Tsirkin wrote:
> > Basically it was very simple: we assumed page->lru was never
> > touched for an allocated page, so it's safe to use it for
> > internal book-keeping by the driver.
> > 
> > Now, this is not the case anymore, you add some logic in mm/ that might
> > or might not touch page->lru depending on things like reference count.
> 
> Another thought: would the issue go away if balloon used
> page->private to link pages instead of LRU?
> mm core could keep a reference on page to avoid it
> being used while mm handles it (maybe it does already?).
>
I don't think so. That would be a lot more trikier and complex, IMHO.
 
> If we do this, will not the only change to balloon be to tell mm that it
> can use compaction for these pages when it allocates the page: using
> some GPF flag or a new API?
> 

What about keep a conter at virtio_balloon structure on how much pages are
isolated from balloon's list and check it at leak time?
if the counter gets > 0 than we can safely put leak_balloon() to wait until
balloon page list gets completely refilled. I guess that is simple to get
accomplished and potentially addresses all your concerns on this issue.

Cheers!

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