Re: [PATCH] Process Aggregates (PAGG) support for the 2.6 kernel

From: Shailabh
Date: Fri Apr 30 2004 - 12:54:59 EST


Christoph Hellwig wrote:
On Fri, Apr 30, 2004 at 08:54:08AM -0400, Rik van Riel wrote:

What was the last time you looked at the CKRM source?


the day before yesterday (the patch in SuSE's tree because there
doesn't seem to be any official patch on their website)


Sure it's a bit bigger than PAGG, but that's also because
it includes the functionality to change the group a process
belongs to and other things that don't seem to be included
in the PAGG patch.


Again, pagg doesn't even play in that league. It's really just a tiny
meachnism to allow a kernel module keep per-process data.

Speaking of per-process data, one of the classification engines of CKRM called crbce, implemented as a module, allows per-process data to be sent to userland. crbce in particular, exports data on the delays seen by processes in a) waiting for cpu time after being runnable b) page fault service time c) io service time etc. (getting the data requires another kernel patch)....so per-process data needs can be met through CKRM, though that is not the intent or main objective of the project.


Policies
like process-groups can be implemented ontop of that.

This is true if one is only interested in data gathering or coarse-grain control. One could monitor per-process stats and fiddle with each process' rlimits (assuming all the ones needed are available) and achieve coarse-grain group control.

But if processes leave and join process groups rapidly, you need the schedulers and the core kernel to be aware of the groupings and schedule resources accordingly.

In CKRM, the premise is that the privileged user defines the way processes get grouped and could do so in a way that leads to rapid changes in group membership. So having group control/monitoring policies implemented as an externally loaded module (not talking of scheduler modifications as modules, which is a no-no) is not a palatable option.


-- Shailabh
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