linux-kernel - Re: [RFC v4 03/15] vfs,hot_track: add the function for collecting I/O frequency

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Date:	Mon, 29 Oct 2012 10:14:39 +0800
From:	Zhi Yong Wu <zwu.kernel@...il.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxram@...ux.vnet.ibm.com, viro@...iv.linux.org.uk,
	tytso@....edu, cmm@...ibm.com,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC v4 03/15] vfs,hot_track: add the function for collecting I/O frequency

On Mon, Oct 29, 2012 at 10:01 AM, Dave Chinner <david@...morbit.com> wrote:
> On Sun, Oct 28, 2012 at 09:51:48PM +0800, Zhi Yong Wu wrote:
>> On Sun, Oct 28, 2012 at 3:55 PM, Zheng Liu <gnehzuil.liu@...il.com> wrote:
>> > Hi Zhiyong,
>> >
>> > On Thu, Oct 25, 2012 at 11:08:55PM +0800, zwu.kernel@...il.com wrote:
>> > [snip]
>> >> @@ -199,6 +342,54 @@ err:
>> >>  }
>> >>
>> >>  /*
>> >> + * Main function to update access frequency from read/writepage(s) hooks
>> >> + */
>> >> +inline void hot_update_freqs(struct inode *inode, u64 start,
>> >> +                     u64 len, int rw)
>> >
>> > This function seems too big.  So we really need to inline this function?
>> As Dave said in his comments, it will add a function call
>> overhead even when tracking is not enabled. a static inline function
>> will just result in no extra overhead other than the if
>> statement....
>
> I don't think I said that with respect to this code. I think I said
> it w.r.t. a define or a small wrapper that decides to call
> hot_update_freqs().  A static inline fucntion should only be a
> couple of lines of code at most.
>
> A static function, OTOH, can be inlined by the compiler if the
> compiler thinks that is a win. But....
thanks for your explaination at first.
>
> .....
>
>> >> +EXPORT_SYMBOL_GPL(hot_update_freqs);
>
> ... it's an exported function, so it can't be inline or static, so
> using "inline" is wrong whatever way you look at it. ;)
ah, but i' m surprised by why the compiler find this error.

>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@...morbit.com
> --
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-- 
Regards,

Zhi Yong Wu
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