[Letux-kernel] Nokia N900 not hitting OFF mode since 5.9 is caused by proactive memory compaction

Andreas Kemnade andreas at kemnade.info
Sat Dec 11 12:14:33 CET 2021


On Fri, 10 Dec 2021 13:39:28 +0100
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> Hi Andreas,
> I have checked:
> 	http://download.goldelico.com/letux-kernel/letux-5.10.83/src/FULLCONFIG
> But
> 	http://download.goldelico.com/letux-kernel/letux-5.10.83/src/DEFCONFIG
> has not. So it needs to be disabled explicitly. Interestingly letux-5.4.163 has it enabled as well.
> So we should also look if the patch identified by Merlijn was already backported...
> Since I can't test it (have no proper power-management-test-setup any more),
> I will proactively disable it for letux-5.10.y, letux-5.15.y and letux-5.16-rc...
For a distribution kernel I am a bit unsure if that is a good idea.
Lets look at Kconfig

          Compaction is the only memory management component to form
          high order (larger physically contiguous) memory blocks
          reliably. The page allocator relies on compaction heavily and
          the lack of the feature can lead to unexpected OOM killer
          invocations for high order memory requests. You shouldn't
          disable this option unless there really is a strong reason for
          it and then we would be really interested to hear about that at
          linux-mm at kvack.org.

ok, the reason is power management. I will recheck things with
a recent kernel but with the gta04 I have not seen these extreme things
and it is also not about suspend current. I guess there is something
special with the N900. People have seen off-mode on omap3 after thet
compaction thing. Anyways, if we do not have a well-crafted module
blacklist, we have some peripherals which are not idling properly, so
runtime pm is not that aggressive anyways on the gta04.


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