linux-kernel - Re: [PATCH 3/7] sysfs: Keep an nlink count on sysfs directories.

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Date:	Mon, 11 Jan 2010 19:53:08 -0500
From:	Benjamin LaHaise <bcrl@...et.ca>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	linux-fsdevel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Serge Hallyn <serue@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 3/7] sysfs: Keep an nlink count on sysfs directories.

On Tue, Jan 12, 2010 at 09:46:59AM +0900, Tejun Heo wrote:
> Hello,
> 
> On 01/12/2010 05:21 AM, Eric W. Biederman wrote:
> > On large directories sysfs_count_nlinks can be a significant
> > bottleneck, so keep a count in sysfs_dirent.
> 
> I was about to suggest changing s_flags to ushort too.  Hmmm... adding
> a new field to sysfs_dirent somewhat worries me but this doesn't add
> to the size of the structure.  How significant bottlenect are we
> talking about?

100,000 entries in a sysfs directory is a requirement for network devices.

> > If we exceed the maximum number of directory entries we can store
> > return nlink of 1.  An nlink of 1 matches what reiserfs does in this
> > case, and it let's find and similar utlities know that we have a the
> > directory nlink can not be used for optimization purposes.
> 
> Hmmm... what's the limit on reiserfs?  Is it 64k too?

64k is too small.  10 gig interfaces can currently service 50-100k users, 
each of which requires their own network device.

		-ben
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