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b=PQHN6d70ELrN3toH2TcI45DI/G35aRETlgWeripiFftg7n1f3wItLYTdAiL6XcdU7 bIou2KquSsNFB2kkrZvgJJ5bO0EA7BJTLiLrTWCZJXtTdB97Nu3YrDBfjyYz7RP3GL gH3aOyXxcR5Cb+IgAMaHDHCT4bSCL5i217xbDQK3cA25va6um9p5upgf3kRawBu87R 6HwwWYNR8B00JgePqDy6EYgpf6tbu2PcxH3Y0bEPXz4FbUS9jokKvAPEuV+khMvKRw l5PFM2D5oKdE/hpJEj2xylh05fzWWStMNiUv5f3y5fjDfWVAreM1ylu2dXMg7ngL40 sjp9XBzoYXw5w== Message-ID: Date: Thu, 26 Feb 2026 18:43:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/3] virtio_balloon: Set pr_dev.order to new default To: Yuvraj Sakshith , akpm@linux-foundation.org, mst@redhat.com Cc: vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, virtualization@lists.linux.dev, kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, longli@microsoft.com, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260226070125.3732265-1-yuvraj.sakshith@oss.qualcomm.com> <20260226070125.3732265-4-yuvraj.sakshith@oss.qualcomm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 470322000D X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 7uzsgpzy61zuodsxhk96oxwhmceufdjd X-HE-Tag: 1772127831-485122 X-HE-Meta: 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 2R/kez6B 81wlefoKjHtDnjiEcD32kbDoYNZMIPR8TXFzFjb+A0e0d23AhMsQT18KBsc4OWBbDjJZmdRV4VChbaANNB0B6YbHId01cwUUeg2dmtMGmzoDFUHDp8xTJKgLC0UnV35yyXrXOTciRor7cExxaG9RgBuDBDjeGtud7RZN8irmSVa/WGfEfz6+Ez61hDn7irMR8aMYAetG2BvyPz4dfWl+1Qwqzt1ICQKASd5Z46zN9FwPMKw/6ZrJw4Lov9tBMkOXSzc2enCnhlSI/c1zCNBJYsipwxZT+mjkOJoT2pMUciqKZ+HZjhfzjLCV0TguGYzjbFZFigU/9LHXROK58ZBp46ndEEg6fiM/anHVxgi+nm1rWCoU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/26/26 08:01, Yuvraj Sakshith wrote: > 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 > --- > 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; That overly-long comment indicates that we can do better. What about the following: Patch #1: Introduce PAGE_REPORTING_DEFAULT_ORDER diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h index fe648dfa3a7c..3e21bfbb49a4 100644 --- a/include/linux/page_reporting.h +++ b/include/linux/page_reporting.h @@ -8,6 +8,9 @@ /* This value should always be a power of 2, see page_reporting_cycle() */ #define PAGE_REPORTING_CAPACITY 32 +/* Specifying this value as minimal reporting order selects the default. */ +#define PAGE_REPORTING_DEFAULT_ORDER 0 + struct page_reporting_dev_info { /* function that alters pages to make them "reported" */ int (*report)(struct page_reporting_dev_info *prdev, diff --git a/mm/page_reporting.c b/mm/page_reporting.c index f0042d5743af..d5191cb6b31c 100644 --- 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_DEFAULT_ORDER && + prdev->order <= MAX_PAGE_ORDER) page_reporting_order = prdev->order; else page_reporting_order = pageblock_order; Patch #2: Use the define in hyperv Patch #3: Use the define in virtio-balloon Patch #4: Change PAGE_REPORTING_DEFAULT_ORDER to "MAX_PAGE_ORDER + 1" or sth. like that. Then I think you can just drop the comment in virtballoon_probe() completely. -- Cheers, David