+ mm-page_reporting-allow-zero-page_reporting_order.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm/page_reporting: allow zero page_reporting_order
has been added to the -mm mm-new branch.  Its filename is
     mm-page_reporting-allow-zero-page_reporting_order.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_reporting-allow-zero-page_reporting_order.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

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------------------------------------------------------
From: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
Subject: mm/page_reporting: allow zero page_reporting_order
Date: Wed, 25 Feb 2026 23:01:23 -0800

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

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 patchset 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 3):

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.

Link: https://lkml.kernel.org/r/20260226070125.3732265-1-yuvraj.sakshith@oss.qualcomm.com
Link: https://lkml.kernel.org/r/20260226070125.3732265-2-yuvraj.sakshith@oss.qualcomm.com
Signed-off-by: Yuvraj Sakshith <yuvraj.sakshith@oss.qualcomm.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: David Hildenbrand <david@kernel.org>
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: Long Li <longli@microsoft.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
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>
---

 mm/page_reporting.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page_reporting.c~mm-page_reporting-allow-zero-page_reporting_order
+++ a/mm/page_reporting.c
@@ -370,7 +370,7 @@ int page_reporting_register(struct page_
 	 */
 
 	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;
_

Patches currently in -mm which might be from yuvraj.sakshith@oss.qualcomm.com are

mm-page_reporting-allow-zero-page_reporting_order.patch
hv_balloon-change-default-page-reporting-order.patch
virtio_balloon-set-pr_devorder-to-new-default.patch