Re: [PATCH v2 4/8] selftests/mm: Add -Wunused family of flags

From: Muhammad Usama Anjum <usama.anjum@collabora.com>
To: Kevin Brodsky <kevin.brodsky@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: usama.anjum@collabora.com, kernel@collabora.com,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Vlastimil Babka <vbabka@suse.cz>,
	Albert Ou <aou@eecs.berkeley.edu>, Zi Yan <ziy@nvidia.com>,
	David Hildenbrand <david@redhat.com>,
	Suren Baghdasaryan <surenb@google.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	Mike Rapoport <rppt@kernel.org>, Peter Xu <peterx@redhat.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Ryan Roberts <ryan.roberts@arm.com>,
	Leon Romanovsky <leon@kernel.org>, Shuah Khan <shuah@kernel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	Alexandre Ghiti <alex@ghiti.fr>, Barry Song <baohua@kernel.org>,
	Dev Jain <dev.jain@arm.com>,
	linux-kselftest@vger.kernel.org,
	Paul Walmsley <paul.walmsley@sifive.com>,
	linux-mm@kvack.org, Nico Pache <npache@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH v2 4/8] selftests/mm: Add -Wunused family of flags
Date: Thu, 21 Aug 2025 17:31:21 +0500	[thread overview]
Message-ID: <4abd97fe-412d-4e3e-9efc-cf3092d66e57@collabora.com> (raw)
In-Reply-To: <88ea592c-c6ff-4a19-a366-eadeca66b039@arm.com>

On 8/21/25 3:43 PM, Kevin Brodsky wrote:
> On 21/08/2025 08:28, Muhammad Usama Anjum wrote:
>>> As to -Wunused-parameter I am frankly not convinced it's worth the
>>> hassle. We're getting 90 lines changed in patch 6-8 just to mark
>>> parameters as unused, in other words noise to keep the compiler happy.
>>> It is not enabled by default in the kernel proper precisely because it
>>> is so noisy when callbacks are involved.
>>>
>>> Patch 5 is clearly an improvement, but I'd rather take it without
>>> actually enabling -Wunused-parameter. The rest of this patch isn't that
>>> useful either IMHO.
>> Patch 5 removes genuinely unused parameters flagged by the compiler. If we
>> drop the -Wunused-parameter option, however, new unused parameters will
>> continue to creep in with future patches. The goal of enabling this warning
>> is to surface such issues early so developers can address them during
>> development, rather than later during review or debugging.
>>
>> Long term, I’d like us to rely more on compiler and static analysis just like
>> kernel to catch these kinds of problems proactively, instead of waiting until
>> they’re reported or someone fixes them later. While it may feel like noise
>> initially, this is largely a one-time cleanup—once done, developers will
>> simply fix warnings as they arise, keeping the codebase cleaner going forward.
> 
> Agreed on the general principle, but I think the hassle is just too big
> for what we're getting in return here (see also Andrew's reply). New
> code may also introduce a bunch of unused parameters for legitimate
> reasons and it's easy to imagine contributors ignoring such seemingly
> harmless/irrelevant warnings instead of sprinkling __unused all over.

> My
> feeling is that unused parameters are expected to be allowed in the
> kernel and it isn't helpful to go against that expectation in just a
> small subset of kselftests.
I thought kernel must be giving error for unused parameters as well (from
my memory). But just checked and it doesn't seem like it. I'm okay with
dropping -Wunused-parameters.

We need to drop patch 6/7 and in Patch 4 should have only:

-CFLAGS += -Wunused  -Wunused-parameter -Wunused-function -Wunused-label -Wunused-variable -Wunused-value
+CFLAGS += -Wunused

@Andrew, Should I resend the entire series or would you can make the change?

> 
> - Kevin

-- 
---
Thanks,
Usama

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