Re: [RFC 0/6] Backing Store for sysfs

[Dipankar Sarma <dipankar@in.ibm.com>]

On Mon, Oct 06, 2003 at 09:08:46AM -0700, Greg KH wrote:
> On Mon, Oct 06, 2003 at 02:29:15PM +0530, Maneesh Soni wrote:
> > 
> > 				2.6.0-test6		With patches.
> > -----------------
> > dentry_cache (active)		2520			2544
> > inode_cache (active)		1058			1050
> > LowFree			875032 KB		874748 KB
> 
> So with these patches we actually eat up more LowFree if all sysfs
> entries are searched, and make the dentry_cache bigger?  That's not good :(

My guess is that those 24 dentries are just noise. What we should
do is verify with a large number of devices if the numbers are all
that different after a walk of the sysfs tree.

> 
> Remember, every kobject that's created will cause a call to
> /sbin/hotplug which will cause udev to walk the sysfs tree to get the
> information for that kobject.  So I don't see any savings in these
> patches, do you?

Assuming that unused files/dirs are aged out of dentry and inode cache,
it should benefit. The numbers you should look at are -

--------------------------------------------------------
After mounting sysfs
-------------------
dentry_cache (active)           2350                    1321
inode_cache (active)            1058                    31
LowFree                         875096 KB               875836 KB
--------------------------------------------------------

That saves ~800KB. If you just mount sysfs and use a few files, you
aren't eating up dentries and inodes for every file in sysfs. How often 
do you expect hotplug events to happen in a system ? Some time after a 
hotplug event, dentries/inodes will get aged out and then you should see 
savings. It should greatly benefit in a normal system.

Now if the additional kobjects cause problems with userland hotplug, then 
that needs to be resolved. However that seems to be a different problem 
altogether. Could you please elaborate on that ?

Thanks
Dipankar