On Fri 02-10-20 09:53:05, Rik van Riel wrote: > On Fri, 2020-10-02 at 09:03 +0200, Michal Hocko wrote: > > On Thu 01-10-20 18:18:10, Sebastiaan Meijer wrote: > > > (Apologies for messing up the mailing list thread, Gmail had fooled > > > me into > > > believing that it properly picked up the thread) > > > > > > On Thu, 1 Oct 2020 at 14:30, Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Wed 30-09-20 21:27:12, Sebastiaan Meijer wrote: > > > > > > yes it shows the bottleneck but it is quite artificial. Read > > > > > > data is > > > > > > usually processed and/or written back and that changes the > > > > > > picture a > > > > > > lot. > > > > > Apologies for reviving an ancient thread (and apologies in > > > > > advance for my lack > > > > > of knowledge on how mailing lists work), but I'd like to offer > > > > > up another > > > > > reason why merging this might be a good idea. > > > > > > > > > > From what I understand, zswap runs its compression on the same > > > > > kswapd thread, > > > > > limiting it to a single thread for compression. Given enough > > > > > processing power, > > > > > zswap can get great throughput using heavier compression > > > > > algorithms like zstd, > > > > > but this is currently greatly limited by the lack of threading. > > > > > > > > Isn't this a problem of the zswap implementation rather than > > > > general > > > > kswapd reclaim? Why zswap doesn't do the same as normal swap out > > > > in a > > > > context outside of the reclaim? > > On systems with lots of very fast IO devices, we have > also seen kswapd take 100% CPU time without any zswap > in use. Do you have more details? Does the saturated kswapd lead to pre-mature direct reclaim? What is the saturated number of reclaimed pages per unit of time? Have you tried to play with this to see whether an additional worker would help? -- Michal Hocko SUSE Labs
