mm/page_reporting: add PAGE_REPORTING_ORDER_UNSPECIFIED

Patch series "Allow order zero pages in page reporting", v4.

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().

This patch (of 5):

Drivers can pass order of pages to be reported while registering itself.
Today, this is a magic number, 0.

Label this with PAGE_REPORTING_ORDER_UNSPECIFIED and check for it when the
driver is being registered.

This macro will be used in relevant drivers next.

[akpm@linux-foundation.org: tweak whitespace, per David]
Link: https://lkml.kernel.org/r/20260303113032.3008371-1-yuvraj.sakshith@oss.qualcomm.com
Link: https://lkml.kernel.org/r/20260303113032.3008371-2-yuvraj.sakshith@oss.qualcomm.com
Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Eugenio Pérez <eperezma@redhat.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Long Li <longli@microsoft.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h
index fe648dfa3a7caef9ab262ad52d321362f4312ff4..d1886c65728591d75ea7391015d50730c2e6c0c1 100644 (file)
--- a/include/linux/page_reporting.h
+++ b/include/linux/page_reporting.h
@@ -7,6 +7,7 @@
 
 /* This value should always be a power of 2, see page_reporting_cycle() */
 #define PAGE_REPORTING_CAPACITY                32
+#define PAGE_REPORTING_ORDER_UNSPECIFIED       0
 
 struct page_reporting_dev_info {
        /* function that alters pages to make them "reported" */

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index f0042d5743af8ff50cfbf938b6a9c6a1c37114ea..a2da5bf3a065b8feb42fd1bce4b3ac9d6017809e 100644 (file)
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -370,7 +370,8 @@ 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 != PAGE_REPORTING_ORDER_UNSPECIFIED &&
+                   prdev->order <= MAX_PAGE_ORDER)
                        page_reporting_order = prdev->order;
                else
                        page_reporting_order = pageblock_order;