Message-ID: <55A94BD2.5040603@gmail.com>
Date: Fri, 17 Jul 2015 14:39:14 -0400
From: Austin S Hemmelgarn <ahferroin7@gmail.com>
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To: Oleg Nesterov <oleg@redhat.com>
CC: Benjamin LaHaise <bcrl@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joonsoo Kim <js1304@gmail.com>, Fengguang Wu <fengguang.wu@intel.com>,
        Jeff Moyer <jmoyer@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>, linux-next@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm-move-mremap-from-file_operations-to-vm_operations_struct-fix
References: <20150716231405.GA25147@redhat.com> <20150716162444.26425f5e227387f1166a6d16@linux-foundation.org> <20150716235227.GA26551@redhat.com> <20150717140615.GA2779@kvack.org> <20150717172726.GA30443@redhat.com> <20150717173757.GD2779@kvack.org> <20150717175542.GA31888@redhat.com> <55A94578.5050306@gmail.com> <20150717181940.GA946@redhat.com>
In-Reply-To: <20150717181940.GA946@redhat.com>
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On 2015-07-17 14:19, Oleg Nesterov wrote:
> On 07/17, Austin S Hemmelgarn wrote:
>>
>> On 2015-07-17 13:55, Oleg Nesterov wrote:
>>> On 07/17, Benjamin LaHaise wrote:
>>>>
>>>> Don't add BUG().  It's the equivalent approach of saying "I think th=
is code
>>>> isn't needed, but I'm lazy and not going to remove it properly."
>>>
>>> There is another interpretation: I think this code must be never call=
ed,
>>> if it is actually called we have a serious problem which should be lo=
udly
>>> reported.
>>>
>> And not compiling it at all _will_ loudly report it, it'll just report=

>> it during linking instead of at run-time, which is a much better time =
to
>> shout about it.
>
> And how can we do this?
>
If a function that isn't defined (for example, you use a #if block to=20
comment it out under certain circumstances), then the link will fail=20
rather noisily something references it.  We already know during the=20
compile that it's a NOMMU kernel, so anything that calls it on a MMU=20
enabled kernel can have a compile time check added instead of doing the=20
check at runtime (or even just calling it without checking), thus even=20
further reducing code size.


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