On Thu, Feb 18, 2016 at 03:15:43PM -0500, Rik van Riel wrote: > On Thu, 2016-02-18 at 11:41 -0500, 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. > > > > On a 140G machine, this raises the default watermark steps - the > > distance between min and low, and low and high - from 16M to 143M. > > This is an excellent idea for a large system, > but your patch reduces the gap between watermarks > on small systems. > > On an 8GB zone, your patch halves the gap between > the watermarks, and on smaller systems it would be > even worse. You're right, I'll address that in v2. > Would it make sense to keep using the old calculation > on small systems, when the result of the old calculation > exceeds that of the new calculation? > > Using the max of the two calculations could prevent > the issue you are trying to prevent on large systems, > from happening on smaller systems. Yes, I think enforcing a reasonable minimum this way makes sense. Thanks Rik. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>