linux-kernel - Re: XFS: Fine-tuning for checks before the function call "xfs_qm

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Message-ID: <20150702001951.GX22807@dastard>
Date:	Thu, 2 Jul 2015 10:19:51 +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: XFS: Fine-tuning for checks before the function call
 "xfs_qm_dqrele"?

On Wed, Jul 01, 2015 at 09:50:00AM +0200, SF Markus Elfring wrote:
> > 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...
> 
> Would it make sense to annotate checks before such function calls
> as "LIKELY"?

No - it will be random as to whether the inodes have dquots attached
or not and so a static hint is always going to be wrong for
someone....

Cheers,

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