Memory load control tuning

Memory load control is intended to smooth out infrequent peaks in load that might otherwise cause the system to thrash.

Memory load control trades multiprogramming for throughput and is not intended to act continuously in a configuration that has too little RAM to handle its normal workload. The design was made for batch jobs and is not very discriminating. The AIX Workload Manager provides a better solution to protect critical tasks.

The correct solution to a fundamental, persistent RAM shortage is to add RAM, not to experiment with memory load control in an attempt to trade off response time for memory. The situations in which the memory-load-control facility may really need to be tuned are those in which there is more RAM, not less than the defaults were chosen for. An example would be configurations in which the defaults are too conservative.

You should not change the memory load control parameter settings unless your workload is consistent and you believe the default parameters are ill-suited to your workload.

The default parameter settings shipped with the system are always in force unless changed. The default values of these parameters have been chosen to "fail safe" across a wide range of workloads. Changed parameters last only until the next system boot. All memory load control tuning activities must be done by the root user. The system administrator can use the schedo command to change the parameters to tune the algorithm to a particular workload or to disable it entirely.

# schedo -a
           v_repage_hi = 0
         v_repage_proc = 4
            v_sec_wait = 1
         v_min_process = 2
         v_exempt_secs = 2
              pacefork = 10
               sched_D = 16
               sched_R = 16
             timeslice = 1
               maxspin = 1
              %usDelta = 100
          affinity_lim = n/a
idle_migration_barrier = n/a
      fixed_pri_global = n/a
         big_tick_size = 1
             force_grq = n/a

The first five parameters specify the thresholds for the memory load control algorithm. These parameters set rates and thresholds for the algorithm. If the algorithm shows that RAM is overcommitted, the v_repage_proc, v_min_process, v_sec_wait, and v_exempt_secs values are used. Otherwise, these values are ignored. If memory load control is disabled, these latter values are not used.

After a tuning experiment, memory load control can be reset to its default characteristics by executing the command schedo -D.