On Mon, Jun 21, 2021 at 10:49 PM Gavin Shan <gshan@xxxxxxxxxx> wrote: > > The page reporting won't be triggered if the freeing page can't come > up with a free area, whose size is equal or bigger than the threshold > (page reporting order). The default page reporting order, equal to > @pageblock_order, is too huge on some architectures to trigger page > reporting. One example is ARM64 when 64KB base page size is used. > > PAGE_SIZE: 64KB > pageblock_order: 13 (512MB) > MAX_ORDER: 14 > > This specifies the page reporting order to 5 (2MB) for this specific > case so that page reporting can be triggered. > > Cc: Michael S. Tsirkin <mst@xxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx> > --- > drivers/virtio/virtio_balloon.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 510e9318854d..fd419780cc23 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -993,6 +993,23 @@ static int virtballoon_probe(struct virtio_device *vdev) > goto out_unregister_oom; > } > > + /* > + * The default page reporting order is @pageblock_order, which > + * corresponds to 512MB in size on ARM64 when 64KB base page > + * size is used. The page reporting won't be triggered if the > + * freeing page can't come up with a free area like that huge. > + * So we specify the page reporting order to 5, corresponding > + * to 2MB. It helps to avoid THP splitting if 4KB base page > + * size is used by host. > + * > + * Ideallh, the page reporting order is selected based on the "Ideally" > + * host's base page size. However, it needs more work to report > + * that value. The hardcoded order would be fine currently. > + */ > +#if defined(CONFIG_ARM64) && defined(CONFIG_ARM64_64K_PAGES) > + vb->pr_dev_info.order = 5; > +#endif > + > err = page_reporting_register(&vb->pr_dev_info); > if (err) > goto out_unregister_oom; This works for now. However my preference would be to look into seeing if we can add a value that the host can report that would override the value you selected here. Then in situations where the host has a smaller THP page size then the guest it can report the preferred reporting order via the virtio_balloon interface and have greater flexibility. Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx>
