On 08/15/2012 04:38 AM, Konrad Rzeszutek Wilk wrote: > On Fri, Aug 10, 2012 at 01:14:01PM -0500, Seth Jennings wrote: >> On 08/09/2012 03:20 PM, Dan Magenheimer wrote >>> I also wonder if you have anything else unusual in your >>> test setup, such as a fast swap disk (mine is a partition >>> on the same rotating disk as source and target of the kernel build, >>> the default install for a RHEL6 system)? >> >> I'm using a normal SATA HDD with two partitions, one for >> swap and the other an ext3 filesystem with the kernel source. >> >>> Or have you disabled cleancache? >> >> Yes, I _did_ disable cleancache. I could see where having >> cleancache enabled could explain the difference in results. > > Why did you disable the cleancache? Having both (cleancache > to compress fs data) and frontswap (to compress swap data) is the > goal - while you turned one of its sources off. I excluded cleancache to reduce interference/noise from the benchmarking results. For this particular workload, cleancache doesn't make a lot of sense since it will steal pages that could otherwise be used for storing frontswap pages to prevent swapin/swapout I/O. In a test run with both enabled, I found that it didn't make much difference under moderate to extreme memory pressure. Both resulted in about 55% I/O reduction. However, on light memory pressure with 8 and 12 threads, it lowered the I/O reduction ability of zcache to roughly 0 compared to ~20% I/O reduction without cleancache. In short, cleancache only had the power to harm in this case, so I didn't enable it. Seth -- 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>