Re: [PATCH 21/63] sched: Update NUMA hinting faults once per scan

[Rik van Riel]

On 10/07/2013 06:28 AM, Mel Gorman wrote:
> NUMA hinting fault counts and placement decisions are both recorded in the
> same array which distorts the samples in an unpredictable fashion. The values
> linearly accumulate during the scan and then decay creating a sawtooth-like
> pattern in the per-node counts. It also means that placement decisions are
> time sensitive. At best it means that it is very difficult to state that
> the buffer holds a decaying average of past faulting behaviour. At worst,
> it can confuse the load balancer if it sees one node with an artifically high
> count due to very recent faulting activity and may create a bouncing effect.
> 
> This patch adds a second array. numa_faults stores the historical data
> which is used for placement decisions. numa_faults_buffer holds the
> fault activity during the current scan window. When the scan completes,
> numa_faults decays and the values from numa_faults_buffer are copied
> across.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>


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