Re: Nokia N900 not hitting OFF mode since 5.9 is caused by proactive memory compaction

[Tony Lindgren <tony@atomide.com>]

* Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> [220103 14:45]:
> Hi,
> 
> On 10.12.21 г. 9:20 ч., Tony Lindgren wrote:
> > Hi,
> > 
> > * Merlijn Wajer <merlijn@wizzup.org> [211210 00:34]:
> > > Hi,
> > > 
> > > I've spent the day bisecting what exact commit prevented the Nokia N900
> > > from entering the OFF sleep state (between v5.8 and v5.9), and it this
> > > commit:
> > > 
> > > > # first bad commit: [facdaa917c4d5a376d09d25865f5a863f906234a] mm: proactive compaction
> > > 
> > > The git tree prior to that commit can idle at about ~27mW in OFF mode,
> > > and it will often remain in that mode for prolonged amounts of time
> > > (easily 30 seconds, depending on running userspace). Which the above
> > > commit applied, the Nokia N900 almost never hits OFF mode any more. This
> > > would suggest at least to disable CONFIG_COMPACTION, perhaps in
> > > omap2plus_defconfig? I suspect this might cause idle problems beyond the
> > > Nokia N900, too.
> > 
> > Nice find, adding Nitin to Cc as well. Nitin, can we somehow avoid the
> > timers for CONFIG_COMPACTION on an idle system to prevent waking up the
> > system unnecessarily?
> > 
> > Not sure if sysctl -w vm.compaction_proactiveness=0 is enough to disable
> > compaction for idle, maybe also the HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500
> > at ms also causes extra wake-ups?
> > 
> 
> This doesn't seem to affect Nokia N900 only, waking-up twice a second will
> have negative effect on power usage of every device this runs on. Could we
> have some discussion on how to avoid that?

Just following up on this as I had it tagged in my inbox.

There's kernel commit 65d759c8f9f5 ("mm: compaction: support triggering of
proactive compaction by user") that should fix this issue.

It seems to require the the following to disable compaction:

# echo 0 > /proc/sys/vm/compaction_proactiveness

Merlijn, care to check if this fixes the issue you're seeing? Or are threre
possibly other bugs too preventing n900 from properly idling?

Regards,

Tony