From: Gavin Shan <gshan@xxxxxxxxxx>
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/20210625014710.42954-5-gshan@xxxxxxxxxx
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
--- 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;
_
