On Mon, 22 Feb 2016, Johannes Weiner wrote: > In machines with 140G of memory and enterprise flash storage, we have > seen read and write bursts routinely exceed the kswapd watermarks and > cause thundering herds in direct reclaim. Unfortunately, the only way > to tune kswapd aggressiveness is through adjusting min_free_kbytes - > the system's emergency reserves - which is entirely unrelated to the > system's latency requirements. In order to get kswapd to maintain a > 250M buffer of free memory, the emergency reserves need to be set to > 1G. That is a lot of memory wasted for no good reason. > > On the other hand, it's reasonable to assume that allocation bursts > and overall allocation concurrency scale with memory capacity, so it > makes sense to make kswapd aggressiveness a function of that as well. > > Change the kswapd watermark scale factor from the currently fixed 25% > of the tunable emergency reserve to a tunable 0.001% of memory. > > Beyond 1G of memory, this will produce bigger watermark steps than the > current formula in default settings. Ensure that the new formula never > chooses steps smaller than that, i.e. 25% of the emergency reserve. > > On a 140G machine, this raises the default watermark steps - the > distance between min and low, and low and high - from 16M to 143M. > > Signed-off-by: Johannes Weiner <[email protected]> > Acked-by: Mel Gorman <[email protected]>
Acked-by: David Rientjes <[email protected]>
