[LTP] [PATCH 1/2] controllers/cpuacct: skip cpuacct_100_100 on small memory systems

[Cyril Hrubis]

Hi!
> Running cpuacct_100_100 on a system with less than ~4 GB of RAM fails:
> 
>     cpuacct 1 TINFO: timeout per run is 0h 5m 0s
>     cpuacct 1 TINFO: cpuacct: /sys/fs/cgroup/cpu,cpuacct
>     cpuacct 1 TINFO: Creating 100 subgroups each with 100 processes
>     testcases/bin/cpuacct.sh: 0: Cannot fork
> 
> In dmesg:
> 
>     LTP: starting cpuacct_100_100 (cpuacct.sh 100 100)
>     cgroup: fork rejected by pids controller in /user.slice/user-1000.slice/session-1.scope
> 
> It seems system might not handle or not allow that amount of processes,
> so simply skip the test.  The threshold of ~4 GB was found during
> experimenting, so it is not accurate.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> ---
>  testcases/kernel/controllers/cpuacct/cpuacct.sh | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/testcases/kernel/controllers/cpuacct/cpuacct.sh b/testcases/kernel/controllers/cpuacct/cpuacct.sh
> index 323aa7513bf4..2646018d295e 100755
> --- a/testcases/kernel/controllers/cpuacct/cpuacct.sh
> +++ b/testcases/kernel/controllers/cpuacct/cpuacct.sh
> @@ -44,6 +44,20 @@ setup()
>  		tst_brk TCONF "cpuacct not supported on this system"
>  	fi
>  
> +	if [ $max -ge 100 ] && [ $nbprocess -ge 100 ]; then
> +		local memtotal=`awk '/MemTotal/ {print $2}' /proc/meminfo`
> +		if [ $? -eq 0 ]; then
> +			# cpuacct.sh 100 100 will fail if memory is less
> +			# than 4 GB with:
> +			#   testcases/bin/cpuacct.sh: 0: Cannot fork
> +			# Choose some limit of total memory, determined
> +			# with experiments: 3*1024+768 MB = 3932160 kB
> +			if [ $memtotal -lt 3932160 ]; then
> +				tst_brk TCONF "not enough of memory on this system (less than 3840 MB)"
> +			fi
> +		fi
> +	fi
> +

This looks quite hacky and ad-hoc.

First of all MemTotal is not a good estimate of usable system memory, if
nothing else this should use better estimate. We have something that is
more or less usable in swapping01.c tests in init_meminfo() function.

Secondly we should create a rough estimage how the memory grows based on
number of processes and on number of subgroups.

The we can have a generic check if there is enough memory for a given
test. The problem is that all these estimates are rough and rest of the
system may eat memory as well, so we will have to make sure there is big
enough margin. If we want to count on the test success it has to be
large and consists "offset" (N * pagesize) and percentage of available
memory 10% or so.

And yes, this is a complex problem that is not easy to fix. If it was
easy it would have been fixed a long time ago...

-- 
Cyril Hrubis
chrubis@suse.cz