[PATCH 0/3] Allow order zero pages in page reporting

[PATCH 0/3] Allow order zero pages in page reporting

[Yuvraj Sakshith]

Today, page reporting sets page_reporting_order in two ways:

(1) page_reporting.page_reporting_order cmdline parameter
(2) Driver can pass order while registering itself.

In both cases, order zero is ignored by free page reporting
because it is used to set page_reporting_order to a default
value, like MAX_PAGE_ORDER.

In some cases we might want page_reporting_order to be zero.

For instance, when virtio-balloon runs inside a guest with
tiny memory (say, 16MB), it might not be able to find a order 1 page
(or in the worst case order MAX_PAGE_ORDER page) after some uptime.
Page reporting should be able to return order zero pages back for
optimal memory relinquishment.

This patch changes the default fallback value from '0' to '-1' in
all possible clients of free page reporting (hv_balloon and
virtio-balloon) together with allowing '0' as a valid order in
page_reporting_register().

Yuvraj Sakshith (3):
  mm/page_reporting: Allow zero page_reporting_order
  hv_balloon: Change default page reporting order
  virtio_balloon: Set pr_dev.order to new default

 drivers/hv/hv_balloon.c         |  2 +-
 drivers/virtio/virtio_balloon.c | 14 ++++++++++++++
 mm/page_reporting.c             |  2 +-
 3 files changed, 16 insertions(+), 2 deletions(-)

-- 
2.34.1

[PATCH 1/3] mm/page_reporting: Allow zero page_reporting_order

[Yuvraj Sakshith]

Some drivers might require page sized chunks to be
reported. This patch allows registering a driver with
order as  zero.

Example use case: virtio-balloon driver running on a
guest with very small memory. After some time has passed,
the guest might not be able to find a chunk of 8KB.

Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
---
 mm/page_reporting.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index e4c428e61..fd7c5f0de 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -370,7 +370,7 @@ int page_reporting_register(struct page_reporting_dev_info *prdev)
 	 */
 
 	if (page_reporting_order == -1) {
-		if (prdev->order > 0 && prdev->order <= MAX_PAGE_ORDER)
+		if (prdev->order >= 0 && prdev->order <= MAX_PAGE_ORDER)
 			page_reporting_order = prdev->order;
 		else
 			page_reporting_order = pageblock_order;
-- 
2.34.1

[PATCH 2/3] hv_balloon: Change default page reporting order

[Yuvraj Sakshith]

page_reporting_order used to fall back to default
value (passed as parameter or MAX_PAGE_ORDER) if
the driver wishes to not provide it.

The way the driver used to do this was by passing
the order as zero.

Now that zero is a valid order that can be passed by
a driver to page reporting, we use -1 to signal
default value to be used.

Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
---
 drivers/hv/hv_balloon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 2b4080e51..e33d6e3b2 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1663,7 +1663,7 @@ static void enable_page_reporting(void)
 	 * We let the page_reporting_order parameter decide the order
 	 * in the page_reporting code
 	 */
-	dm_device.pr_dev_info.order = 0;
+	dm_device.pr_dev_info.order = -1;
 	ret = page_reporting_register(&dm_device.pr_dev_info);
 	if (ret < 0) {
 		dm_device.pr_dev_info.report = NULL;
-- 
2.34.1

[PATCH 3/3] virtio_balloon: Set pr_dev.order to new default

[Yuvraj Sakshith]

Drivers registering with page reporting used zero
as a way to signal page_reporting_order to be set
as a default value (either passed as a param or
MAX_PAGE_ORDER).

Since page_reporting_order can now have zero as
valid order, default fallback value send by drivers
to page reporting is now -1.

Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
---
 drivers/virtio/virtio_balloon.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 74fe59f5a..3cc3dc28a 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -1044,6 +1044,20 @@ static int virtballoon_probe(struct virtio_device *vdev)
 			goto out_unregister_oom;
 		}
 
+		/*
+		 * page_reporting_register() takes the order either
+		 * from the driver or the commandline. If neither
+		 * are provided, it falls back to MAX_PAGE_ORDER.
+		 *
+		 * Order given by the driver is required to be in the
+		 * range [0, MAX_PAGE_ORDER].
+		 *
+		 * One way for the driver to not provide any order
+		 * is by setting it to -1.
+		 */
+
+		vb->pr_dev_info.order = -1;
+
 		/*
 		 * The default page reporting order is @pageblock_order, which
 		 * corresponds to 512MB in size on ARM64 when 64KB base page
-- 
2.34.1