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Michael S. Tsirkin
47c81dadb7
At the moment, if a virtio balloon device has a page reporting vq but its
size is < PAGE_REPORTING_CAPACITY (32), the balloon driver fails probe.
But, there's no way for host to know this value, so it can easily create a
smaller vq and suddenly adding the reporting capability to the device
makes all of the driver fail. Not pretty.
Add a capacity field to page_reporting_dev_info so drivers can control the
maximum number of pages per report batch.
In virtio-balloon, set the capacity to the reporting virtqueue size,
letting page_reporting adapt to whatever the device provides.
Capacity need not be a power of two. Code previously called out division
by PAGE_REPORTING_CAPACITY as cheap since it was a power of 2, but no
performance difference was observed with non-power-of-2 values.
If capacity is 0 or exceeds PAGE_REPORTING_CAPACITY, it defaults to
PAGE_REPORTING_CAPACITY. The 0 check and the clamping is done in
page_reporting_register(), before the reporting work is scheduled, so we
never get division by 0.
Link: https://lore.kernel.org/444c24cf39f3f3620fc90ef4695bd6b0979f4c4b.1783232420.git.mst@redhat.com
Fixes: b0c504f154 ("virtio-balloon: add support for providing free page reports to host")
Signed-off-by: Michael S. Tsirkin <[email protected]>
Assisted-by: Claude:claude-opus-4-6
Acked-by: David Hildenbrand (Arm) <[email protected]>
Reviewed-by: Gregory Price <[email protected]>
Acked-by: Zi Yan <[email protected]>
Reviewed-by: Pankaj Gupta <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Brendan Jackman <[email protected]>
Cc: Eugenio Pérez <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>