Re: [PATCH 2/2] mirror throttling

[Alasdair G Kergon]

On Wed, Jan 09, 2013 at 12:44:38AM -0500, Mikulas Patocka wrote:
> We maintain a history of kcopyd usage in variables io_period and
> total_period. The actual kcopyd activity is "(100 * io_period /
> total_period)" percent of time. If we exceed user-defined percentage
> threshold, we sleep.
 
Well, I'm going to take this pair of patches for now.

Some people do need this throttling today and this seems to me to be a
decent and simple way to give them a lever to deal with the problem.

I'm not proposing we expose this through LVM or other userspace tools at
this stage: people who need it should tune it directly through sysfs.

If need be, we can revisit this in future either by refining the
algorithm or making it adjustable per-device rather than per-module.
(Or by re-vamping kcopyd itself...)

The current version is:
  http://people.redhat.com/agk/patches/linux/editing/dm-kcopyd-introduce-configurable-throttling.patch

Alasdair

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