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Subject: Re: [PATCH 2/2] fs/dcache: Make negative dentries easier to be
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To: Andrew Morton <akpm@linux-foundation.org>,
 Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>, Al Viro <viro@zeniv.linux.org.uk>,
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References: <1535476780-5773-1-git-send-email-longman@redhat.com>
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 <6873378b-3202-e738-2366-5fb818b4a013@redhat.com>
 <CA+55aFxy1vH2CamZ_pdFohKgSJgi1i2MkeaY1qX8NdFK8Xu8Ww@mail.gmail.com>
 <20180828162207.52240d3442fbe65166f9d604@linux-foundation.org>
From: Waiman Long <longman@redhat.com>
Message-ID: <a7c7150f-9e8e-62d3-6dac-0b86a2f69876@redhat.com>
Date: Tue, 28 Aug 2018 21:18:56 -0400
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On 08/28/2018 07:22 PM, Andrew Morton wrote:
> On Tue, 28 Aug 2018 16:10:24 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> On Tue, Aug 28, 2018 at 3:29 PM Waiman Long <longman@redhat.com> wrote:
>>> Yes, I can rewrite it. What is the problem with the abbreviated form?
>> Either gcc rewrites it for you, or you end up _actually_ using a
>> function pointer and calling through it.
>>
>> The latter would be absolutely horribly bad for something like
>> "list_add()", which should expand to just a couple of instructions.
>>
>> And the former would be ok, except for the "you wrote code the garbage
>> way, and then depended on the compiler fixing it up". Which we
>> generally try to avoid in the kernel.
>>
>> (Don't get me wrong - we definitely depend on the compiler doing a
>> good job at CSE and dead code elimination etc, but generally we try to
>> avoid the whole "compiler has to rewrite code to be good" model).
>>
> And the "abbreviated form" will surely explode if one or both of those
> "functions" happens to be implemented (or later reimplemented) as a macro.
> It's best not to unnecessarily make such assumptions.
>
Yes,  that is true.

Thanks,
Longman