On Thu, Nov 22, 2018 at 03:59:26PM +0900, Sergey Senozhatsky wrote: > On (11/22/18 15:31), Minchan Kim wrote: > > > > > > I got what you mean now. Let's call it as "incompressible page wrieback" > > > to prevent confusing. > > > > > > "incompressible page writeback" would be orthgonal feature. The goal is > > > "let's save memory at the cost of *latency*". If the page is swapped-in > > > soon, it's unfortunate. However, the design expects once it's swapped out, > > > it means it's non-workingset so soonish swappined-in would be rather not > > > many, theoritically compared to other workingset. > > > If's it's too frequent, it means system were heavily overcommitted. > > > > Havid said, I agree it's not a good idea to enable incompressible page > > writeback with idle page writeback. If you don't oppose, I want to add > > new knob to "enable incompressible page writeback" so by default, > > although we enable CONFIG_ZRAM_WRITEBACK, incompressible page writeback > > is off until we enable the knob. > > It would make some regressison if someone have used the feature but > > I guess we are not too late. > > > > What do you think? > > Yes, totally works for me! > > > "IDLE writeback" is superior to "incompressible writeback". > > "incompressible writeback" is completely unpredictable and > uncontrollable; it depens on data patterns and compression algorithms. > While "IDLE writeback" is predictable. > > I even suspect, that, *ideally*, we can remove "incompressible > writeback". "IDLE pages" is a super set which also includes > "incompressible" pages. So, technically, we still can do > "incompressible writeback" from "IDLE writeback" path; but a much > more reasonable one, based on a page idling period. > > I understand that you want to keep "direct incompressible writeback" > around. ZRAM is especially popular on devices which do suffer from > flash wearout, so I can see "incompressible writeback" path becoming > a dead code, long term.
Okay, both options makes regression if someone use it. Then, let's try to remove it. It would make more clean with new idle writeback. Thanks!
