On Mon, 2020-10-05 at 13:32 -0400, Rik van Riel wrote: > 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: > > 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%. Never mind that. On larger tests the effect seems to disappear, probably because the logic in __swapin_nr_pages() already reduces the number of pages read ahead to 2 on workloads with lots of random access. That reduces the latency effects observed. Now we might still see some memory waste due to decompressing pages we don't need, but I have not seen any real effects from that yet, either. I think it may be time to focus on a larger memory waste with zswap: leaving the compressed copy of memory around when we decompress the memory at swapin time. More aggressively freeing the compressed memory will probably buy us more than reducing readahead. -- All Rights Reversed.
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