On Wed, Mar 07, 2018 at 02:47:09PM +0530, Vinayak Menon wrote: > > This needs a proper changelog, signed-offs and a comment on the reasoning > > behind the new min value for the gap between low and high and how it > > was derived. It appears the equation was designed such at the gap, as > > a percentage of the zone size, would shrink according as the zone size > > increases but I'm not 100% certain that was the intent. That should be > > explained and why not just using "tmp >> 2" would have problems. > > > > It would also need review/testing by Johannes to ensure that there is no > > reintroduction of the problems that watermark_scale_factor was designed > > to solve. > > Sorry for the delayed response. I will send a patch with the details. The equation was designed so that the > low-high gap is small for smaller RAM sizes and tends towards min-low gap as the RAM size increases. This > was done considering that it should not have a bad effect on for 140G configuration which Johannes had taken > taken as example when watermark_scale_factor was introduced, also assuming that the thrashing seen due to > low-high gap would be visible only on low RAM devices. > If you do spin a new version with corrections made, be very careful to note that the figures you supply are based on a kernel without THP because that's where it makes a real difference. The differences with THP enabled are very different as that alters min_free_kbytes and by extention, it changes the point where your patch has an effect on the distance between watermarks. It does mean that a test you say definitely works will not necessary be visible to someone who tests the same patch on x86-64. Maybe no one will notice or care but if you get a report about the results being unreproducible then I suggest you check first if THP was enabled. -- Mel Gorman SUSE Labs -- 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>
