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SubjectMemory-compaction not working on Atmel SAMA5 ARM platform, kernel v4.14 and v4.20
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Hello all,


Memory-compaction is not working for me on an Atmel SAMA5D2 SoC with
128Mbyte of RAM, on kernel versions 4.14.73. 4.14.88 and 4.20.0

Using "cat /proc/buddyinfo" to observe the state of memory
fragmentation, and "echo 1 > /proc/sys/vm/compact_memory" to (try to)
trigger compaction.

My kernel's /proc/config.gz includes "CONFIG_COMPACTION=y" and
"CONFIG_MIGRATION=y"

I have rebuilt v4.20 several++ times, enabling various "CONFIG_xxx"
items trying to enable tracing, but without success
(/sys/kernel/debug/tracing is not present), so I haven't been able to
observe whether the compaction-trigger is having any effect at all.


Some circumstantial evidence: memory-compaction was working on another
ARM platform (Raspberry Pi) with kernel v4.9 (Raspbian Jessie), but
stopped working when I dist-upgraded it to v4.14.98 (Raspbian Stretch). 
The "
/proc/sys/vm/compact_memory" device-node is present, but writing to it
has no effect on the output from "cat /proc/buddyinfo".


So my questions are:

1.  Are "CONFIG_COMPACTION=y" + "CONFIG_MIGRATION=y" the only settings
necessary for memory-compaction to be present and working in a kernel? 
I have Done My Own Research, but Am Not An Expert on Linux kernel features!

2.  Must I persevere with trying to get tracing working, or is there
another way I can debug this issue?


Thank you,

Mike Haben

ASH Wireless

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