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SubjectRe: [PATCH v8 1/5] mm: introduce a common interface for balloon pages mobility
On Tue, Aug 21, 2012 at 04:52:23PM +0300, Michael S. Tsirkin wrote:
> > + * address_space_operations utilized methods for ballooned pages:
> > + * .migratepage - used to perform balloon's page migration (as is)
> > + * .launder_page - used to isolate a page from balloon's page list
> > + * .freepage - used to reinsert an isolated page to balloon's page list
> > + */
>
> It would be a good idea to document the assumptions here.
> Looks like .launder_page and .freepage are called in rcu critical
> section.
> But migratepage isn't - why is that safe?
>

The migratepage callback for virtio_balloon can sleep, and IIUC we cannot sleep
within a RCU critical section.

Also, The migratepage callback is called at inner migration's circle function
move_to_new_page(), and I don't think embedding it in a RCU critical section
would be a good idea, for the same understanding aforementioned.



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