[041/192] virtio_balloon: specify page reporting order if needed

Commit Message

Andrew Morton June 29, 2021, 2:35 a.m. UTC

From: Gavin Shan <[e-mail]>
Subject: virtio_balloon: specify page reporting order if needed

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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Gavin Shan <[e-mail]>
Reviewed-by: Alexander Duyck <[e-mail]>
Cc: Michael S. Tsirkin <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Anshuman Khandual <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 drivers/virtio/virtio_balloon.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Patch

--- a/drivers/virtio/virtio_balloon.c~virtio_balloon-specify-page-reporting-order-if-needed
+++ a/drivers/virtio/virtio_balloon.c
@@ -993,6 +993,23 @@  static int virtballoon_probe(struct virt
 			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.
+		 *
+		 * Ideally, the page reporting order is selected based on the
+		 * host's base page size. However, it needs more work to report
+		 * that value. The hard-coded 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;