From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B28FB3290A6; Thu, 26 Feb 2026 17:43:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772127830; cv=none; b=nBDVv8hqgjl9DI9ef3sFzbCoAL6l4mbhlits2AHvmkWKD+fgB4sUg1aks3Q7od9StAMzhecBo6xsDsnAy02WbWysujI1LDv7seQ10i3O8pajOK0/eNPLvubVug01tQJAFJuWY7CRuONa1JNjblMjTmvARNjM5o42TeoJ3jqT+Sk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772127830; c=relaxed/simple; bh=P8ldSxwfLZVjMH586whroUmxuPZFLnNzibkezo9KuFQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iGonUrQZOEVsp58APLKh/TDkB+/NnwsE7Z8jjX9HLPddDXurpotgisfwaKtvd2ylQtOA8Cl9ABD4BsIyb3l2sS1+xIxkVwWuV5pNT+72wS6WSPTm+Gn6acEuPrXk1KLnRHY6F8Nqhc4uDqTwCpLJhX/tlsUQ6SGl3fqym0kCK68= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PQHN6d70; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PQHN6d70" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68B34C116C6; Thu, 26 Feb 2026 17:43:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772127830; bh=P8ldSxwfLZVjMH586whroUmxuPZFLnNzibkezo9KuFQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PQHN6d70ELrN3toH2TcI45DI/G35aRETlgWeripiFftg7n1f3wItLYTdAiL6XcdU7 bIou2KquSsNFB2kkrZvgJJ5bO0EA7BJTLiLrTWCZJXtTdB97Nu3YrDBfjyYz7RP3GL gH3aOyXxcR5Cb+IgAMaHDHCT4bSCL5i217xbDQK3cA25va6um9p5upgf3kRawBu87R 6HwwWYNR8B00JgePqDy6EYgpf6tbu2PcxH3Y0bEPXz4FbUS9jokKvAPEuV+khMvKRw l5PFM2D5oKdE/hpJEj2xylh05fzWWStMNiUv5f3y5fjDfWVAreM1ylu2dXMg7ngL40 sjp9XBzoYXw5w== Message-ID: Date: Thu, 26 Feb 2026 18:43:42 +0100 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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 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