zram on ARM

[Luigi Semenzato <semenzato@google.com>]

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Does anybody have any information on the status of zram on ARM?
Specifically, how much it has been tested.

I noticed that zram and zsmalloc on ToT no longer have the x86
restriction, and they compile fine on our 3.4 branch.  Sadly, that's
where my luck ends.

When I run my standard Chrome load (which just opens a bunch of
memory-intensive browser tabs), Chrome dies shortly after the system
starts swapping pages out.  For instance, here's are the SI and SO
fields of "vmstat 1":

   si   so
    0    0
    0    0
    0    0
    0    0
    0    0
    0    0
    0    0
    0    0
    0  168
    0    0
    0  924
  188 26332
  520 30672
 1304 32208
 2360 30804
 18836 24832
                     <--- chrome dies here
 6496    0
  892    0
  260    0
    8    0

I also have a simpler load: a program that allocates memory non-stop,
and fills part of it with data from /dev/urandom (to simulate the
observed compressibility). The program never reads its data though, so
it doesn't get swapped back in, as in the previous load.  This runs
for a while and partially fills the swap device, then the system
hangs.

Deja vu, eh?  I am running this with my patch, which may result in
extra OOM kills.  Interestingly, a few threads are blocked in
exit_mm(), but not on a page fault.  Most processes are in
congestion_wait(), so this is probably not the same situation I was
seeing earlier.

Anyway, I am attaching the output of SysRQ-X with lots of stack
traces.  Thank you very much for any information!

Luigi

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