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

[Christian Borntraeger]

> Hi,
> 
> The following patch set(mailed separately) provides a prototype for a 
backing 
> store mechanism for sysfs. Currently sysfs pins all its dentries and 
inodes in 
> memory there by wasting kernel lowmem even when it is not mounted. 
> 
> With this patch set we create sysfs dentry whenever it is required like 
> other real filesystems and, age and free it as per the dcache rules. We
> now save significant amount of Lowmem by avoiding un-necessary pinning. 

A more mature patch could be a possible solution of some problems we faced 
with sysfs.
I have s390 test system with ~ 20000 devices. Memory consumption _without_ 
this
patch is horribly high.
Slab uses 346028 kB of memory, most of it is dentry and inode cache. 
I tried the patch, its boots, memory usage is much better,  but it is 
somewhat 
broken with our ccw devices as I cannot bring up our ccwgroup network 
devices. 
Therefore I dont have reliable memory results.
Almost nobody would use 20000 devices on a S390, but with some shared 
OSA-card
100 or 200 devices is realistic. Even in this case, memory consumption is 
much higher
than with 2.4.

I still have to look closer on this patch, if there are some deeper 
problems. 
Until I find something, I think this patch could be really helpful for 
computers with lots of devices.

-- 
Mit freundlichen Grüßen / Best Regards

Christian Bornträger
IBM Deutschland Entwicklung GmbH
eServer SW  System Evaluation + Test
email: CBORNTRA@xxxxxxxxxx
Tel +49  7031 16 1975

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