On Tue, 2020-09-22 at 10:12 -0700, Andrew Morton wrote: > On Mon, 21 Sep 2020 22:01:46 -0400 Rik van Riel <riel@xxxxxxxxxxx> > wrote: > > > Both with frontswap/zswap, and with some extremely fast IO devices, > > swap IO will be done before the "asynchronous" swap_readpage() call > > has returned. > > > > In that case, doing swap readahead only wastes memory, increases > > latency, and increases the chances of needing to evict something > > more > > useful from memory. In that case, just skip swap readahead. > > Any quantitative testing results? I have test results with a real workload now. Without this patch, enabling zswap results in about an 8% increase in p99 request latency. With these patches, the latency penalty for enabling zswap is under 1%. Enabling zswap allows us to give the main workload a little more memory, since the spikes in memory demand caused by things like system management software no longer cause large latency issues. -- All Rights Reversed.
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