Hi! On Sat, Jun 06, 2020 at 01:15:35AM -0700, Samuel Sieb wrote: > 5GB of swap space that normally would be on disk is now taking less than 2G > of RAM. Instead of the usual 6G in the disk swap, now I have less than 2.
What's bugging me about this thread is that quite a few people made comparisions resulting in "compressed zram is smaller than uncompressed disk swap". For me this seems quite obvious, and looks like flawed testing. Wouldn't it be more correct to also compress disk swap to compare size? This would probably make the size-argument void, as I'd expect them to be the same size. If it's not, that would be an useful data point. Also I don't care about 10GB stuff sitting in disk swap, whilst 1GB of RAM could be quite essential. This leaves overall performance as a potential benefit of zram swap. What almost noone wrote about is CPU usage, for which I saw two anecdotal references: "no change" and "doubled CPU usage". It would be interesting to see a comparison of swap, compressed swap and zram swap performance while having processes competing on swap. E.g. System with 8 GB RAM: * 2 processes with 3.5 GB memory each this would leave about 1GB for the system itself, so with disk swap there should be not much swapping and with zram swap I'd expect little swapping too. * 2 processes with 4 GB memory each this would force light disk swap usage in the first two cases, I'm not really sure what it would do to zram swap. * 2 processes with 4.5 GB memory each this would definitely lead to constant swapping, but it should still fit in zram swap, with a ratio of 2:1 it should theoretically fit in a 2GB zram device, and realistically in a 4GB zram device. For the programs I'd think of something allocating memory and writing/reading random parts of it, running for N iterations. Interesting points would be: average CPU usage and wallclock time for each of the processes. I've left out the obvious cases of "not enough memory usage to use any of those anyway" and "too much memory usage that it results in oom". oom killer should not invoke in daily usage anyway, I see that as a sign for "something has gone seriously wrong", comparable with "program segfaults on start". All the best, David
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