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

Benjamin LaHaise
2010-01-12T01:15:08Z

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