linux-kernel - Re: [PATCH 2/2] fs/dcache: Make negative dentries easier to be reclaimed

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Date:   Tue, 28 Aug 2018 21:18:56 -0400
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>, Jan Kara <jack@...e.cz>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "Wangkai (Kevin,C)" <wangkai86@...wei.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH 2/2] fs/dcache: Make negative dentries easier to be
 reclaimed

On 08/28/2018 07:22 PM, Andrew Morton wrote:
> On Tue, 28 Aug 2018 16:10:24 -0700 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> On Tue, Aug 28, 2018 at 3:29 PM Waiman Long <longman@...hat.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