Fedora 26 / Kernel 4.11.10 - System becomes unresponsive when swapping

[Steven Haigh]

Hi all,

Firstly, please CC me directly in replies due to not being subscribed.

After a fix to glibc that fixed Unity 3D based games (Fedora ref: https://
bugzilla.redhat.com/show_bug.cgi?id=1440287), I have noticed that when I play 
Cities: Skylines that the system becomes unresponsive when digging into swap.

I have 10Gb of RAM in this system and run Fedora 26. If I launch Cities: 
Skylines with no swap space, things run well performance wise until I get an 
OOM - and it all dies - which is expected.

When I turn on swap to /dev/sda2 which resides on an SSD, I get complete 
system freezes while swap is being accessed.

The first swap was after loading a saved game, then launching kmail in the 
background. This caused ~500Mb to be swapped to /dev/sda2 on an SSD. The 
system froze for about 8 minutes - barely being able to move the mouse. The 
HDD LED was on constantly during the entire time.

To hopefully rule out the above glibc issue, I started the game via jemalloc - 
but experienced even more severe freezes while swapping. I gave up waiting 
after 13 minutes of non-responsiveness - not even being able to move the mouse 
properly.

During these hangs, I could typed into a Konsole window, and some of the 
typing took 3+ minutes to display on the screen (yay for buffers?).

I have tested this with both the default vm.swappiness values, as well as the 
following:
vm.swappiness = 1
vm.min_free_kbytes = 32768
vm.vfs_cache_pressure = 60

I noticed that when I do eventually get screen updates, all 8 cpus (4 cores / 
2 threads) show 100% CPU usage - and kswapd is right up there in the process 
list for CPU usage. Sadly I haven't been able to capture this information 
fully yet due to said unresponsiveness.

This seems to be a relatively new problem that I did not encounter during the 
Fedora 26 beta - but do now.

Does anyone have any suggestions on where to start tracking this type of issue 
down?

-- 
Steven Haigh

ð netwiz@xxxxxxxxx       ð http://www.crc.id.au
ð +61 (3) 9001 6090    ð 0412 935 897

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