linux-kernel - Re: [PATCH] XFS: Delete unnecessary checks before the function call "xfs_qm

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Message-ID: <20150629214355.GE7943@dastard>
Date:	Tue, 30 Jun 2015 07:43:55 +1000
From:	Dave Chinner <david@...morbit.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:	xfs@....sgi.com, LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH] XFS: Delete unnecessary checks before the function call
 "xfs_qm_dqrele"

On Fri, Jun 26, 2015 at 11:15:31AM +0200, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Fri, 26 Jun 2015 11:05:41 +0200
> 
> The xfs_qm_dqrele() function tests whether its argument is NULL and
> then returns immediately.

True.

> Thus the test around the call is not needed.

But wrong.

xfs_dqrele_inode() gets called on every inode in the inode cache,
and this change results in a cacheline in every inode being dirtied
even if they don't have dquots attached. Given the inode cache can
hold tens to hundreds of millions of inodes on large machines, we
don't want to dirty any cachelines we don't need to while walking
the inode cache and releasing dquots...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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