linux-kernel - [PATCH v5 4/4] virtio_balloon: Specify page reporting order if needed

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Message-Id: <20210625042150.46964-5-gshan@redhat.com>
Date:   Fri, 25 Jun 2021 12:21:50 +0800
From:   Gavin Shan <gshan@...hat.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, alexander.duyck@...il.com,
        david@...hat.com, mst@...hat.com, akpm@...ux-foundation.org,
        anshuman.khandual@....com, catalin.marinas@....com,
        will@...nel.org, shan.gavin@...il.com
Subject: [PATCH v5 4/4] 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.

Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: David Hildenbrand <david@...hat.com>
Cc: virtualization@...ts.linux-foundation.org
Signed-off-by: Gavin Shan <gshan@...hat.com>
Reviewed-by: Alexander Duyck <alexanderduyck@...com>
---
 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..47dce91f788c 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.
+		 *
+		 * 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;
-- 
2.23.0