On Sun, Jul 05, 2026 at 01:16:35AM -0700, Andrew Morton wrote: > On Sun, 5 Jul 2026 02:25:13 -0400 "Michael S. Tsirkin" <[email protected]> > wrote: > > > 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. > > Thanks. What's the priority here? Should we fix 7.2? Earlier?
If possible, I'd like it in 7.2, have a setup like this (small queue is useful for perf testing). It's very early in the cycle and the code seems straight forward... I judge the chances of breaking anything is tiny because it just failed probe previously. > It seems that Sashiko has found a pre-existing issue, a hard-to-hit > error path thing: > > > https://sashiko.dev/#/patchset/444c24cf39f3f3620fc90ef4695bd6b0979f4c4b.1783232420.git....@redhat.com > will look into this, thanks!
