Re: [ckrm-tech] RFC: Memory Controller

[Balbir Singh <balbir@in.ibm.com>]

Paul Menage wrote:
> On 10/31/06, Balbir Singh <balbir@in.ibm.com> wrote:
>> I am still a little concerned about how limit size changes will be implemented.
>> Will the cpuset "mems" field change to reflect the changed limits?
> 
> That's how we've been doing it - increasing limits is easy, shrinking
> them is harder ...
> 
>>> Page cache control is actually more essential that RSS control, in our
>>> experience - it's pretty easy to track RSS values from userspace, and
>>> react reasonably quickly to kill things that go over their limit, but
>>> determining page cache usage (i.e. determining which job on the system
>>> is flooding the page cache with dirty buffers) is pretty much
>>> impossible currently.
>>>
>> Hmm... interesting. Why do you think its impossible, what are the kinds of
>> issues you've run into?
>>
> 
> Issues such as:
> 
> - determining from userspace how much of the page cache is really
> "free" memory that can be given out to new jobs without impacting the
> performance of existing jobs
> 
> - determining which job on the system is flooding the page cache with
> dirty buffers
> 
> - accounting the active pagecache usage of a job as part of its memory
> footprint (if a process is only 1MB large but is seeking randomly
> through a 1GB file, treating it as only using/needing 1MB isn't
> practical).
> 
> Paul
> 

Thanks for the info!

I thought this would be hard to do in general, but with a page -->
container mapping that will come as a result of the memory controller,
will it still be that hard?

I'll dig deeper.

-- 

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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