Re: [PATCH 2/2] fs/dcache: Make negative dentries easier to be reclaimed
From: Waiman Long
Date: Tue Aug 28 2018 - 21:19:02 EST
On 08/28/2018 07:22 PM, Andrew Morton wrote:
> On Tue, 28 Aug 2018 16:10:24 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Tue, Aug 28, 2018 at 3:29 PM Waiman Long <longman@xxxxxxxxxx> 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.