linux-kernel - Re: [PATCH] vfs: remove the unnecessrary code of fs/inode.c

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Message-ID: <51D2719D.8040802@gmail.com>
Date:	Tue, 02 Jul 2013 02:22:21 -0400
From:	Dong Fang <yp.fangdong@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: remove the unnecessrary code of fs/inode.c

On 07/02/2013 02:11 AM, Dong Fang wrote:
> On 07/02/2013 12:41 AM, Al Viro wrote:
>> On Mon, Jul 01, 2013 at 08:19:03AM -0400, Dong Fang wrote:
>>> These functions, such as find_inode_fast() and find_inode(),
>>> iget_lock() and
>>> iget5_lock(), insert_inode_locked() and insert_inode_locked4(),
>>> almost have
>>> the same code.
>>
>> NAK.  These functions exist exactly because the variant with callbacks
>> costs more.  We walk the hash chain and for each inode on it your
>> variant would result in
>>     * call
>>     * fetching ino from memory
>>     * comparison (and storing result in general-purpose register)
>>     * return
>>     * checking that register and branch on the result of that check
>> What's more, the whole thing's not fun for branch predictor.
>>
>> It is a hot enough path to warrant a special-cased variant; if we can't
>> get away with that, we use the variants with callbacks, but on
>> filesystems
>> where ->i_ino is sufficient as search key we really want to avoid the
>> overhead.
>>
>
> that's right, i didn't think of it, but i think may be we can remove
> the deduplicate codes of iget_lock() and iget5_lock() function, right?
>
> if ok, i will send a new patch later. :)
>
> thx Viro.

Viro, regard this :)
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