From: Andrew Morton <akpm@linux-foundation.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Waiman Long <longman@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Jonathan Corbet <corbet@lwn.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Kees Cook <keescook@chromium.org>, Jan Kara <jack@suse.cz>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>,
Larry Woodman <lwoodman@redhat.com>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
"Wangkai (Kevin,C)" <wangkai86@huawei.com>,
Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 2/2] fs/dcache: Make negative dentries easier to be reclaimed
Date: Tue, 28 Aug 2018 16:22:07 -0700 [thread overview]
Message-ID: <20180828162207.52240d3442fbe65166f9d604@linux-foundation.org> (raw)
In-Reply-To: <CA+55aFxy1vH2CamZ_pdFohKgSJgi1i2MkeaY1qX8NdFK8Xu8Ww@mail.gmail.com>
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.
next prev parent reply other threads:[~2018-08-28 23:22 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-28 17:19 [PATCH 0/2] fs/dcache: Track # of negative dentries Waiman Long
2018-08-28 17:19 ` [PATCH 1/2] fs/dcache: Track & report number " Waiman Long
2018-08-29 0:11 ` Dave Chinner
2018-08-29 17:11 ` Waiman Long
2018-08-30 1:43 ` Dave Chinner
2018-08-30 21:49 ` Waiman Long
2018-08-31 14:31 ` Matthew Wilcox
2018-08-31 15:03 ` Waiman Long
2018-08-28 17:19 ` [PATCH 2/2] fs/dcache: Make negative dentries easier to be reclaimed Waiman Long
2018-08-28 22:13 ` Matthew Wilcox
2018-08-28 22:29 ` Waiman Long
2018-08-28 23:10 ` Linus Torvalds
2018-08-28 23:22 ` Andrew Morton [this message]
2018-08-29 1:18 ` Waiman Long
2018-08-29 1:18 ` Waiman Long
2018-08-28 23:01 ` Andrew Morton
2018-08-29 17:54 ` Paul E. McKenney
2018-08-29 20:03 ` Waiman Long
2018-08-29 21:04 ` Matthew Wilcox
2018-08-29 1:02 ` Dave Chinner
2018-08-29 19:34 ` Waiman Long
2018-08-30 1:12 ` Dave Chinner
2018-08-30 21:51 ` Waiman Long
2018-08-29 7:51 ` Michal Hocko
2018-08-29 19:58 ` Waiman Long
2018-08-30 7:20 ` Michal Hocko
2018-08-30 21:48 ` Waiman Long
2018-08-28 22:50 ` [PATCH 0/2] fs/dcache: Track # of negative dentries Andrew Morton
2018-08-28 22:54 ` Waiman Long
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