zram02 in kernel_misc from ubuntu_ltp failed on B / B-5.4 i386

[Po-Hsu Lin]

Issue found on B-hwe-5.3 (5.3.0-53.47~18.04.1) with i386 node pepe (works with other arches)

 startup='Fri May 8 23:50:43 2020'
 zram02 1 TINFO: timeout per run is 0h 5m 0s
 zram02 1 TINFO: create '1' zram device(s)
 zram02 1 TPASS: test succeeded
 zram02 1 TCONF: The device attribute max_comp_streams was introduced in kernel 3.15 and deprecated in 4.7
 zram02 2 TINFO: set disk size to zram device(s)
 sh: echo: I/O error
 zram02 2 TFAIL: can't set '107374182400' to /sys/block/zram0/disksize
 sh: echo: I/O error
 zram02 2 TINFO: AppArmor enabled, this may affect test results
 zram02 2 TINFO: it can be disabled with TST_DISABLE_APPARMOR=1 (requires super/root)
 zram02 2 TINFO: loaded AppArmor profiles: none

 Summary:
 passed 1
 failed 1
 skipped 1
 warnings 0
 tag=zram02 stime=1588981843 dur=0 exit=exited stat=1 core=no cu=2 cs=1

[Po-Hsu Lin (cypressyew)]

Found on i386 node pepe 4.15.0-137.141

[Kelsey Steele (kelsey-steele)]

found on B/hwe 5.4.0-71.79~18.04.1

[Krzysztof Kozlowski (krzk)]

Found on pepe.i386 instances (only):
bionic/linux-hwe-5.4/5.4.0-81.91~18.04.1
bionic/linux-hwe-5.4/5.4.0-84.94~18.04.1

[Thadeu Lima de Souza Cascardo (cascardo)]

I haven't been able to reproduce this on a trusty amd64 3.13.0-187 system, while it failed on a trusty i386 3.13.0-188 system. It also failed on a bionic i386 4.15.0-162 VM.

When running it with dash, it does give I/O Error, but while doing strace with it, it returns ENOMEM and bash does give out the appropriate error message.

echo: write error: Cannot allocate memory

So this looks more like a limitation of zram on 32 bit systems.

Cascardo.

[Thadeu Lima de Souza Cascardo (cascardo)]

Yeah, so vmalloc space is limited to 122880 KiB on the systems I have here, and I don't think it can be any larger on i386. And zram would try to allocate around ~200MiB for this specific request, so there is not even virtual address space enough for this on i386.

Cascardo.