Re: [PATCH v2 3/3] virtio_balloon: Specify page reporting order if needed
From: Alexander Duyck <hidden>
Date: 2021-06-22 17:45:34
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On Mon, Jun 21, 2021 at 10:49 PM Gavin Shan [off-list ref] wrote:
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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@redhat.com> Cc: David Hildenbrand <redacted> Cc: virtualization@lists.linux-foundation.org Signed-off-by: Gavin Shan <redacted> --- 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@fb.com>