[Devel] Re: [RFC][PATCH 7/7] UBC: proc interface

[Kir Kolyshkin]

Greg KH wrote:
> On Thu, Aug 17, 2006 at 05:43:16PM +0400, Kirill Korotaev wrote:
>   
>>> On Wed, Aug 16, 2006 at 07:44:30PM +0400, Kirill Korotaev wrote:
>>>
>>>       
>>>> Add proc interface (/proc/user_beancounters) allowing to see current
>>>> state (usage/limits/fails for each UB). Implemented via seq files.
>>>>         
>>> Ugh, why /proc?  This doesn't have anything to do with processes, just
>>> users, right?  What's wrong with /sys/kernel/ instead?
>>>       
>> We can move it, if there are much objections.
>>     
>
> I am objecting.  /proc is for processes so do not add any new files
> there that do not deal with processes.
>
>   
>>> Or /sys/kernel/debug/user_beancounters/ in debugfs as this is just a
>>> debugging thing, right?
>>>       
>> debugfs is usually OFF imho.
>>     
>
> No, distros enable it.
>
>   
>> you don't export meminfo information in debugfs, correct?
>>     
>
> That is because the meminfo is tied to processes, or was added to proc
> before debugfs came about.
>
> Then how about just /sys/kernel/ instead and use sysfs?  Just remember,
> one value per file please.
>   
I see two problems with that. But let me first describe the current 
/proc/user_beancounters.  This is how it looks like from inside a container:

# cat /proc/user_beancounters
Version: 2.5
       uid  resource           held    maxheld    barrier      limit    failcnt
       123: kmemsize         836919    1005343    2752512    2936012          0
            lockedpages           0          0         32         32          0
            privvmpages        4587       7289      49152      53575          0
............(more lines like that).........................................


I.e. a container owner can take a glance over the current parameters, 
their usage and (the thing that is really important) fail counters. Fail 
counter increases each time a parameter hits the limit. This is very 
straightforward way for container's owner to see if everything is OK or not.

So, the problems with /sys are:

(1) Gettng such info from 40+ files requires at least some script, while 
now cat is just fine.

(2) Do we want to virtualize sysfs and enable /sys for every container? 
Note that user_beancounters statistics is really needed for container's 
owner to see. At the same time, container's owner should not be able to 
modify it -- so we should end up with read/write ubc entries for the 
host system and read-only ones for the container.

Taking into account those two issues, current /proc/user_beancounters 
might be not that bad.