On Tue, 23 Oct 2012, Andrew Morton wrote:
> > I run a bleeding edge gentoo with 2 6-core AMD CPUs. I daily updated
> > 3 gentoo systems on this computer all using -j13. Until recently, I
> > never experienced issues, CPUs may all go neer 100%, no problem.
> >
> > Now, when building icedtea-7, for example, regardless of -j13 or -j1,
> > about 10 javac instances run threaded (either spreaded on multiple or
> > one core) and go to about 1000% CPU together.
> >
> > Nothing else can be started. This can take 24 hours, no improvement.
> >
> > Only one way to recover: kill -9 javac.
> >
> > One time kernel rebooted, I could not find any relevant kernel logs
> > before reboot.
> >
> >
> > I hd noticed khugepaged on top in top (just below 1000% CPU javac)
> > which made me look at HUGEPAGE settings.
> >
> > FWIW, an strace on javac PID showed it doing nothing in futex
> >
> > As said, MADVISE fixes issue.
> >
We'll need to collect some information before we can figure out what the
problem is with 3.5.2.
First, let's take a look at khugepaged. By default, it's supposed to wake
up rarely (10s at minimum) and only scan 4K pages before going back to
sleep. Having a consistent and very high cpu usage suggests the settings
aren't the default. Can you do
cat /sys/kernel/mm/transparent_hugepage/khugepaged/{alloc,scan}_sleep_millisecs
The defaults should be 60000 and 10000, respectively. Then can you do
cat /sys/kernel/mm/transparent_hugepage/khugepaged/pages_to_scan
which should be 4096. If those are your settings, then it seems like
khugepaged in 3.5.2 is going crazy and we'll need to look into that. Try
collecting
grep -e "thp|compact" /proc/vmstat
and
cat /proc/$(pidof khugepaged)/stack
appended to a logfile at regular intervals after your start the build with
transparent hugepages enabled always. After the machine becomes
unresponsive and reboots, post that log.
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