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

Hi Nitin, linux-mm list,

Any ideas or comments on the problem I encountered and on the question
from Tony below? Is it possible to have CONFIG_COMPACTION not wake up
systems unnecessarily, or should it perhaps be disabled for systems
where power consumption is an issue?

Thanks,
Regards,
Merlijn

PS: I already earlier noted in this thread that setting "sysctl -w
vm.compaction_proactiveness=0" does not solve the problem, as the system
stills is kept awake by CONFIG_COMPACTION.

On 10/12/2021 08:20, Tony Lindgren wrote:

Hi,

* Merlijn Wajer [off-list ref] [211210 00:34]:

quoted

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:

quoted

# 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?

Regards,

Tony

quoted

Maybe nothing needs to be done here other than disable the config option
-- but I wanted to share this in case others are trying to figure out
what happened to their battery life. :-)

There seem be more power regressions since then (at least on 5.15 there
is more blocking proper idle), so I'll try to find those as well, but if
this commit is reverted (or CONFIG_COMPACTION=n is in .config - probably
easier) on top of v5.9 the system seems to idle fine.

quoted

# grep ^core_pwrdm /sys/kernel/debug/pm_debug/count | cut -d',' -f2,
OFF:16,RET:2

Hope this helps someone...

Regards,
Merlijn

PS: v5.10 seems to use another 19mW if panel_sony_acx565akm is loaded
even when display is not active (maybe it doesn't suspend or something?
- could be fixed later, just noticed it for v5.10). I load it initially
to idle the display, but until I rmmod the modules, the module uses
quite a bit more power. This problem is not present in v5.9, so that is
another thing to chase down I guess... And then v5.15 uses another 12mW
more, for not yet uncovered reasons)