System crashing when swap hits 25%
Chris Snook
csnook at redhat.com
Mon Mar 10 22:51:38 UTC 2008
Simon Slater wrote:
> G'day all,
> This is an inconvenience that I would like to get to the bottom of. I
> have a PII 233MHz 512 MbRAM running FC6. All is fine until swap reaches
> about 25% used then the system hangs. It will run for days with the
> swap at 10-15%. My first thought was to run badblocks to see if that
> was the problem, since it is an old drive, but couldn't find the swap
> device with mount.
25% of your 1 GB swap space is about 50% of your total RAM. 50% is also
the default value of the vm.overcommit_ratio sysctl, which controls how
optimistically the system overcommits memory. Coincidence? Maybe,
maybe not.
I suggest setting vm.overcommit_memory=2 with sysctl to turn on explicit
overcommit control, and then try changing the value of
vm.overcommit_ratio to see if that changes where your system dies.
Also, is the system actually crashing, or does it just get swaplocked
and hang indefinitely when swap usage reaches 25%? See if you can get
sysrq-m and sysrq-t data out of the system. You'll want to set
kernel.sysrq=1 first.
-- Chris
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