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[129.46.96.20]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4160cf9b240sm10950856fac.8.2026.03.01.19.33.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 01 Mar 2026 19:33:03 -0800 (PST) Date: Sun, 1 Mar 2026 19:33:00 -0800 From: Yuvraj Sakshith To: "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, mst@redhat.com, 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, 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, virtualization@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 4/4] page_reporting: change PAGE_REPORTING_DEFAULT_ORDER to -1 Message-ID: References: <20260227140655.360696-1-yuvraj.sakshith@oss.qualcomm.com> <20260227140655.360696-5-yuvraj.sakshith@oss.qualcomm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Proofpoint-GUID: f8RVOKn_pTJIcLNJUqqKy-9rzhNq9E8d X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAyMDAyOSBTYWx0ZWRfX1Jl5IkkGbJfh sKxU2ep/8ogZrPrZs+WXA804m6eaNIrmqvb/UxGGdOqdnAL6itxJoGyUJvqZcjpOD8SV61ASKbL EP8pb1FHNt1z776xd43oV1Sx8/Hs8kR/awS2NzjUYrz1eMITyp8L8KbMYotE5HdtAchCPkrQwLB eGO92DYyLIXnCwtshSlSAUFJoODQ/mBn3PEPeLwyMHVMRnKG6ZLhQ3rJsVfuCJAsxrlNq3hDFTM TGSVXC06pbZcztFoLtIo7ZYItqOxHsEStU7pI1rAXh6tOtVwnPv59YgGK1rHvzpCbKfdfv8f+gq leViFQxTaHWb68dzQKyxpQ5noj0WyIb3xUsAK211h9LiGuzEqdGM83kQrMKeDAOvXk2C5Xm/tR6 lFZhkgwHUt2RLR4UA0IaSU8JYTY4scESSqKkWbWdKMvpBQrKPwlv/cvu5ApsHPTpzz770b6CnKF Qk32rMpTa37Dojic6iQ== X-Authority-Analysis: v=2.4 cv=bdRmkePB c=1 sm=1 tr=0 ts=69a504f1 cx=c_pps a=WJcna6AvsNCxL/DJwPP1KA==:117 a=ouPCqIW2jiPt+lZRy3xVPw==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yOCtJkima9RkubShWh1s:22 a=EUspDBNiAAAA:8 a=JqjX9IW5vOmFWWUa66MA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=_Y9Zt4tPzoBS9L09Snn2:22 X-Proofpoint-ORIG-GUID: f8RVOKn_pTJIcLNJUqqKy-9rzhNq9E8d X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-02_01,2026-02-27_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 clxscore=1015 malwarescore=0 impostorscore=0 suspectscore=0 adultscore=0 spamscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603020029 On Fri, Feb 27, 2026 at 09:50:15PM +0100, David Hildenbrand (Arm) wrote: > On 2/27/26 15:06, Yuvraj Sakshith wrote: > > PAGE_REPORTING_DEFAULT_ORDER is now set to zero. This means, > > pages of order zero cannot be reported to a client/driver -- as zero > > is used to signal a fallback to MAX_PAGE_ORDER. > > > > Change PAGE_REPORTING_DEFAULT_ORDER to (-1), > > so that zero can be used as a valid order with which pages can > > be reported. > > > > Signed-off-by: Yuvraj Sakshith > > --- > > include/linux/page_reporting.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h > > index a7e3e30f2..3eb3e26d8 100644 > > --- a/include/linux/page_reporting.h > > +++ b/include/linux/page_reporting.h > > @@ -7,7 +7,7 @@ > > > > /* This value should always be a power of 2, see page_reporting_cycle() */ > > #define PAGE_REPORTING_CAPACITY 32 > > -#define PAGE_REPORTING_DEFAULT_ORDER 0 > > +#define PAGE_REPORTING_DEFAULT_ORDER (-1) > > No need for the (). > > Wondering whether we now also want to do in this patch: > > > diff --git a/mm/page_reporting.c b/mm/page_reporting.c > index f0042d5743af..d432aadf9d07 100644 > --- a/mm/page_reporting.c > +++ b/mm/page_reporting.c > @@ -11,8 +11,7 @@ > #include "page_reporting.h" > #include "internal.h" > > -/* Initialize to an unsupported value */ > -unsigned int page_reporting_order = -1; > +unsigned int page_reporting_order = PAGE_REPORTING_DEFAULT_ORDER; > > static int page_order_update_notify(const char *val, const struct > kernel_param *kp) > { > @@ -369,7 +368,7 @@ int page_reporting_register(struct > page_reporting_dev_info *prdev) > * pageblock_order. > */ > > - if (page_reporting_order == -1) { > + if (page_reporting_order == PAGE_REPORTING_DEFAULT_ORDER) { > > Sure. Now that I think of it, don’t you think the first nested if() will always be false? and can be compressed down to just one if()? - if (page_reporting_order == PAGE_REPORTING_DEFAULT_ORDER) { - if (prdev->order != PAGE_REPORTING_DEFAULT_ORDER && - prdev->order <= MAX_PAGE_ORDER) - page_reporting_order = prdev->order; - else - page_reporting_order = pageblock_order; - } + page_reporting_order = pageblock_order; + + if (prdev->order != PAGE_REPORTING_DEFAULT_ORDER && + prdev->order <= MAX_PAGE_ORDER) + page_reporting_order = prdev->order; Thanks, Yuvraj > > (and wondering whether we should have called it > PAGE_REPORTING_USE_DEFAULT_ORDER to make it clearer that it is not an > actual order. Leaving that up to you :) ) > > -- > Cheers, > > David