linux-kernel - Re: [RFCv2][PATCH 1/7] fs: optimize inotify/fsnotify code for unwatched files

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Date:	Thu, 25 Jun 2015 09:28:25 -0700
From:	Dave Hansen <dave@...1.net>
To:	Eric Paris <eparis@...hat.com>
CC:	dave.hansen@...ux.intel.com, akpm@...ux-foundation.org,
	jack@...e.cz, viro@...iv.linux.org.uk, john@...nmccutchan.com,
	rlove@...ve.org, tim.c.chen@...ux.intel.com, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFCv2][PATCH 1/7] fs: optimize inotify/fsnotify code for unwatched
 files

On 06/24/2015 05:57 PM, Eric Paris wrote:
> On Wed, 2015-06-24 at 17:16 -0700, Dave Hansen wrote:
>> +	if (!to_tell->i_fsnotify_marks.first &&
>> +	    (!mnt || !mnt->mnt_fsnotify_marks.first))
>> +		return 0;
> 
> two useless peeps from the old peanut gallery of long lost....
> 
> 1) should you actually move this check up before the IN_MODIFY check?
> This seems like it would be by far the most common case, and you'd save
> yourself a bunch of useless conditionals/bit operations.

Doing that actually makes fsnotify() 82 bytes smaller for me.  I think
you're also right that the new check is a much more general condition
than the existing one.  I'll move it up when I post again.

> 2) do you want to use hlist_empty(&to_tell->i_fsnotify_marks) instead,
> for readability (and they are static inline, so compiled code is the
> same)

Yeah I guess that makes sense.  The only thing that the current code is
nice for is that it makes it obvious that the .first checks match with
the srcu_dereference()s done below.
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