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[80.230.79.166]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-439ba2a5970sm13000276f8f.33.2026.03.03.09.42.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Mar 2026 09:42:58 -0800 (PST) Date: Tue, 3 Mar 2026 12:42:54 -0500 From: "Michael S. Tsirkin" To: Yuvraj Sakshith Cc: david@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, longli@microsoft.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev, linux-mm@kvack.org Subject: Re: [PATCH v4 0/5] Allow order zero pages in page reporting Message-ID: <20260303124236-mutt-send-email-mst@kernel.org> References: <20260303113032.3008371-1-yuvraj.sakshith@oss.qualcomm.com> Precedence: bulk X-Mailing-List: linux-hyperv@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260303113032.3008371-1-yuvraj.sakshith@oss.qualcomm.com> On Tue, Mar 03, 2026 at 03:30:27AM -0800, Yuvraj Sakshith wrote: > 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(). virtio change is a technicality, so Acked-by: Michael S. Tsirkin > Changes in v1: > - Introduce PAGE_REPORTING_DEFAULT_ORDER macro (initially set to 0). > - Make use of new macro in drivers (hv_balloon and virtio-balloon) > working with page reporting. > - Change PAGE_REPORTING_DEFAULT_ORDER to -1 as zero is a valid > page order that can be requested. > > Changes in v2: > - Better naming. Replace PAGE_REPORTING_DEFAULT_ORDER with > PAGE_REPORTING_ORDER_UNSPECIFIED. This takes care of > the situation where page reporting order is not specified > in the commandline. > - Minor commit message changes. > > Changes in v3: > - Setting page_reporting_order's initial value to > PAGE_REPORTING_ORDER_UNSPECIFIED moved to > PATCH #5. > > Changes in v4: > - Move PAGE_REPORTING_ORDER_UNSPECIFIED's usage with > page_reporting_order to patch #5. > > Yuvraj Sakshith (5): > mm/page_reporting: add PAGE_REPORTING_ORDER_UNSPECIFIED > virtio_balloon: set unspecified page reporting order > hv_balloon: set unspecified page reporting order > mm/page_reporting: change PAGE_REPORTING_ORDER_UNSPECIFIED to -1 > mm/page_reporting: change page_reporting_order to > PAGE_REPORTING_ORDER_UNSPECIFIED > > drivers/hv/hv_balloon.c | 2 +- > drivers/virtio/virtio_balloon.c | 2 ++ > include/linux/page_reporting.h | 1 + > mm/page_reporting.c | 7 ++++--- > 4 files changed, 8 insertions(+), 4 deletions(-) > > -- > 2.34.1