Minimum System Requirements

[Eero Tamminen]

Hi,

On keskiviikko 17 heinäkuu 2013, PK wrote:
> Maybe a swappiness decrease can be considered for Xubuntu instead?

Swappiness controls how "early" / "speculatively" kernel starts to swap
memory pages to disk to make more RAM free.  Default is a compromise on
this:

* With higher swappiness you see slowdown earlier, but it's more gradual.

* With lower swappiness you see slowdown later, but then the effect is worse
  (and it can be *much* worse, like hitting a wall).


Although fiddling with swappiness can help in specific cases, it doesn't
help with performance in general, as that completely depends on how well
your typical workload fits into RAM.

If your typical computer tasks keep RAM usage below the threshold where
things turn much worse, lowering swappiness makes machine more responsive
[1]. But if RAM usage now and then goes over that threshold, lowering
swappiness makes machine perform worse.

Because you cannot predict what kind of work loads users of Xubuntu in
general are going to do on their machines, there's not much point in
lowering the default.  While it would make situation better for some
users, it would make it worse for others.


	- Eero

[1] There may be some workloads where speculative swapping is particularly
    inefficent because kernel scheduler cannot predict future and it happens
    to swap out lot of pages that either need to immmediately paged back or
    are discarded.  I'm not sure what such cases would be, but in those
    cases lowering swappiness would definitely increase (at least disk)
    performance.