[dm-devel] [PATCH][enhancement] device-mapper: load-balancing path selector

[Stefan Bader]

This is a patch against Linux kernel 2.6.13 to add another path selecting 
method to
device-mapper: the load-balance selector.

This new selector will keep track of the number of request sent to each
path which have not yet completed. When selecting a new path it will 
choose the one
with the least amount of outstanding requests. In case the number of 
requests is the
same for all paths the behaviour is the same as for the round-robin 
selector (each path
would be used in turn).

The benefits of this approach is that it will evenly spread I/O to all 
paths and
should adapt to paths that are faster or slower.

The load-balance selector accepts one argument which has the same meaning
as for the round-robin selector (the number of requests that are sent to 
the same
path before selection is done).
The status device-mapper call will additionally show the number of 
requests that are
pending.

I tried to keep the changes to common code as small as possible. The 
current
solution requires only one additional function hook which is  called 
whenever a
request is successfully mapped.

Comments are welcome.

Regards,
Stefan Bader

SW Linux on zSeries Development & Services
Stefan.Bader at de.ibm.com
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