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Subject: Re: [RFC PATCH 2/8] mm/madvise: remove unnecessary check on
 madvise_dontneed_free()
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <20210927121902.r5gslag4nvvseoxo@box>
Date:   Mon, 27 Sep 2021 05:52:12 -0700
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Peter Xu <peterx@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Minchan Kim <minchan@kernel.org>,
        Colin Cross <ccross@google.com>,
        Suren Baghdasarya <surenb@google.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>
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References: <20210926161259.238054-1-namit@vmware.com>
 <20210926161259.238054-3-namit@vmware.com>
 <20210927091143.tn6ediykqycu6rtu@box.shutemov.name>
 <DD025444-B1A2-4470-9069-0072A59427A5@gmail.com>
 <20210927121902.r5gslag4nvvseoxo@box>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Precedence: bulk


> On Sep 27, 2021, at 5:19 AM, Kirill A. Shutemov <kirill@shutemov.name> =
wrote:
>=20
> On Mon, Sep 27, 2021 at 04:05:47AM -0700, Nadav Amit wrote:
>> Having said that, if you want, I can turn this condition into
>> WARN_ON_ONCE() or VM_BUG_ON(), although I really see no reason to
>> do so.
>=20
> BUILD_BUG() should be fine here.

It does not work. At least my gcc is not smart enough to figure it
out in build time.

I can put instead:

	BUILD_BUG_ON(__builtin_constant_p(behavior));

for potentially smarter compilers (clang?), but I doubt it would work.