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 16F48383C8D; Mon, 2 Mar 2026 07:43:06 +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=1772437387; cv=none; b=hn0NJVYe1fraH2M3ZFJ8JTR0gTrNSjWwvEu81NMqLAbShZdeE5eKPdgkzB4hIouDpXYJohilJmiYIXVJhuhaVya0u+hvtRBzhs3xVivXpX5pVgtt1liWf9m9TA6X2brqFnwEtROYIH1oFIT5v3zlZzUb631deExyAul/QgE61ng= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772437387; c=relaxed/simple; bh=h4vd67w0fuuMwxwBTUXPN4v+6iOyEsPXL80rum2E98Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MumWsqy0UZZXtOrDGQcJYEhAFBEITc+5XzoWpVGMGVpXb5PkFM6C7I9yXX5yEb+iWljHTFGOh2dc9IGP0NYXuQTxojKfPKSYqWOzCqw51eETkV0envT0z0rZlEMC4wVV+CsQnbmZkwRjIVK1nx/DFM6MUP0rm4lw6c+DLAChsmw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=udKdOqVG; 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="udKdOqVG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 631A3C2BC9E; Mon, 2 Mar 2026 07:43:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772437386; bh=h4vd67w0fuuMwxwBTUXPN4v+6iOyEsPXL80rum2E98Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=udKdOqVGE7twa4wsV/WME0ZgmzBxDsuJltPh8za6s3sw3PeFVrz927G6vaA2WVq2W iZctCtcQFJ5OEae7twJ3AQpNQ3OjUEKiN5ZTNaP6JTn2neCDx8OLoFmhjyXXeRBE4c txUnSJ2LsLSsQRD3e/rqS25lU30zGAWPqjaJ9QkLpyJLGwIjtUEKk0eIiyJtNzTeZZ 0WbV6hp0l+9NmOWL4s5grW3/whTzbJItTI8N13QihXflt7V5mW16iJfcp5DyJAoyG+ 6kX1RTZuz/MiC1DtwgNA1s67dRIy4qrgXiyPd52Jkt/5Ji+3PN99LuMi1xRJ5wP5O7 AmsGeB1Xgng4Q== Message-ID: Date: Mon, 2 Mar 2026 08:42:57 +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: Michael Kelley , Yuvraj Sakshith 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 06:25, Michael Kelley wrote: > From: Yuvraj Sakshith Sent: Sunday, March 1, 2026 7:33 PM >> >> On Fri, Feb 27, 2026 at 09:50:15PM +0100, David Hildenbrand (Arm) wrote: >>> >>> 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()? > > 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. 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. -- Cheers, David