is mapreduce.task.io.sort.mb control both map merge buffer and reduce merge buffer?

[ch huang]

hi,maillist:
              Due to the heavy job on reduce task, i try to increase buffer
size for sort merge,i wander if i increase mapreduce.task.io.sort.mb from
100m(default value) to 1G will cause each map task  sort merge buffer also
become 1G?