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 B4B5434E74F; Mon, 2 Mar 2026 08:09:22 +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=1772438962; cv=none; b=ZFsaAUv8lHfJpNO8iqiCu8s9IzimB4xbu0KV9QgzmKgmj8hWA9UBM346gFBfv5Y4Mt8fZDYm8HNn7KR6ECq6AnrhMcEin3EIcauk+VWr5sH4gQXpYC01lf4dhg9m7mJtHA+i60rU6RNja7pYRn+LAs783OaZjQzWAOj/d+1YCa0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772438962; c=relaxed/simple; bh=FqBCPiof80sYQVn6PUFltJWkTioFCV7WXdE9UKQ7PRc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kyVs6ebqXCE05FH3QKxohTQTjeNb4TkcEILyUdG1JUIXcH7CYlRZYSjaLrGsTQsQSrziVsMaVRgdB1KfKLvYYXBcYhFImwXqEe1eJjtBT68MFqB65zRsyh/qscNxIbSAr3Pzm2NzVGymYR3aMh/QHqAg4ND3AvZteIPBjUBi+hA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TF6xmoM1; 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="TF6xmoM1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35630C19423; Mon, 2 Mar 2026 08:09:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772438962; bh=FqBCPiof80sYQVn6PUFltJWkTioFCV7WXdE9UKQ7PRc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=TF6xmoM1xb1BmDnHJGEYYK4djC4sZPGpc5YK/nAz7HzJ1voYUouiCetVuo4MDwIpB 6zABBzdYxHDeL41uNqVAX1tuBhYFK91ibtgQRO3fwM1RvwD5iMZYlIFEuIDv2pkz/u UfmnJhWi16+xkmfzi4Mr6GzFG0kCrcEryF3fjlWJ94GUjDYfn+xqfI4lLa6y9wv3l2 CDygaFMQ4D+7OXNntYjczvYmpenkTHXU7sBr1ZEaL3BTj5QsLgUPSPuPc0ohEzyIF8 Y6Fv8UYd+pvl01YZ4KQwdKLNNBRMW0+MN0Wc1pYz4LP9dyabdnwudPjvSu3mkYbDAu mI4cxujLVJIAA== Message-ID: Date: Mon, 2 Mar 2026 09:09:13 +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 v1 4/4] page_reporting: change PAGE_REPORTING_DEFAULT_ORDER to -1 To: Yuvraj Sakshith , Michael Kelley 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" References: <20260227140655.360696-1-yuvraj.sakshith@oss.qualcomm.com> <20260227140655.360696-5-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: 8bit On 3/2/26 09:00, Yuvraj Sakshith wrote: > On Mon, Mar 02, 2026 at 08:42:57AM +0100, David Hildenbrand (Arm) wrote: >> On 3/2/26 06:25, Michael Kelley wrote: >>> From: Yuvraj Sakshith Sent: Sunday, March 1, 2026 7:33 PM >>> >>> I don't think what you propose is correct. The purpose of testing >>> page_reporting_order for -1 is to see if a page reporting order has >>> been specified on the kernel boot line. If it has been specified, then >>> the page reporting order specified in the call to page_reporting_register() >>> [either a specific value or the default] is ignored and the kernel boot >>> line value prevails. But if page_reporting_order is -1 here, then >>> no kernel boot line value was specified, and the value passed to >>> page_reporting_register() should prevail. >>> >>> With this in mind, substituting PAGE_REPORTING_DEFAULT_ORDER >>> for the -1 in the test doesn’t exactly make sense to me. The -1 in the >>> test doesn't have quite the same meaning as the -1 for >>> PAGE_REPORTING_DEFAULT_ORDER. You could even use -2 for >>> the initial value of page_reporting_order, and here in the test, in >>> order to make that distinction obvious. Or use a separate symbolic >>> name like PAGE_REPORTING_ORDER_NOT_SET. >> > Option 1: > > if (page_reporting_order == PAGE_REPORTING_DEFAULT_ORDER) { > if (page_reporting_order != PAGE_REPORTING_DEFAULT_ORDER > && prdev->order <= MAX_PAGE_ORDER) { > page_reporting_order = prdev->order; > } else { > page_reporting_order = pageblock_order; > } > } > > Option 2: > > if (page_reporting_order == PAGE_REPORTING_ORDER_NOT_SET) { > if (page_reporting_order != PAGE_REPORTING_DEFAULT_ORDER > && prdev->order <= MAX_PAGE_ORDER) { > page_reporting_order = prdev->order; > } else { > page_reporting_order = pageblock_order; > } > } > > >> I don't really see a difference between "PAGE_REPORTING_DEFAULT_ORDER" >> and "PAGE_REPORTING_ORDER_NOT_SET" that would warrant a split and adding >> confusion for the page-reporting drivers. >> >> In both cases, we want "no special requirement, just use the default". >> Maybe we can use a better name to express that. > > Agreed. > > If we were to read this code without context, wouldn't it be confusing as to > why PAGE_REPORTING_DEFAULT_ORDER is being checked in the first place? I proposed in one of the last mail that "PAGE_REPORTING_USE_DEFAULT_ORDER" could be clearer, stating that it's not really an order just yet. Maybe just using PAGE_REPORTING_ORDER_UNSET might be clearer. > > Option 1 checks if page_reporting_order is equal to PAGE_REPORTING_DEFAULT_ORDER > and then immediately checks if its not equal to it. Which is a bit confusing.. Because it's wrong? :) We're not supposed to check page_reporting_order a second time. Assume we s/PAGE_REPORTING_ORDER/PAGE_REPORTING_ORDER_UNSET/ and actually check prdev->order: if (page_reporting_order == PAGE_REPORTING_ORDER_UNSET) { if (prdev->order != PAGE_REPORTING_ORDER_UNSET && prdev->order <= MAX_PAGE_ORDER) { page_reporting_order = prdev->order; } else { page_reporting_order = pageblock_order; } } -- Cheers, David