Nick Piggin wrote:
On Thursday 01 November 2007 12:56, bc Wong (chimwong) wrote:
Hi,
With 2.6.16 x86_64 on a 4 core machine, I noticed
that the filp usage (according to /proc/slabinfo)
shoots up and keeps on increasing sharply when one
of the CPUs is (1) locked up, or (2) very busy
doing a lot of printk()'s with KERN_EMERG.
In the case of (1), it's permanent until it runs
out of memory eventually. For (2), it's temporary;
filp count comes back down when the printk()'s are
done.
I can't think of any relationship between a busy/
locked-up CPU and filp count. The system is still
functional. New short-lived processes kept being
created, but the overall number of processes is
stable.
Does anyone know why filp count would go up like
that?
Yeah, it's probably because filp structures are freed by
RCU, and if you have a locked up CPU then it can't go
through a quiescent state so RCU stops freeing your filps.
If you add some cond_resched()s to your code, you should
find that RCU will force a reschedule and things will work
(actually, for 2.6.16, I'm not sure if RCU had the code to
force a reschedule... it's force_quiescent_state() in
kernel/rcupdate.c upstream).
Thanks! You're absolutely right. Btw, 2.6.16 does
have force_quiescent_state().
Cheers,
bc
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