Re: Root-causing kswapd spinning on Sandy Bridge laptops?

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Andi Kleen's message of 2011-06-24 14:44:12 -0400:
> Andrew Lutomirski <luto@mit.edu> writes:
> 
> [Putting the Intel graphics driver developers in cc.]
> 
> > I'm back :-/
> >
> > I just triggered the kswapd bug on 2.6.39.1, which has the
> > cond_resched in shrink_slab.  This time my system's still usable (I'm
> > tying this email on it), but kswapd0 is taking 100% cpu.  It *does*
> > schedule (tested by setting its affinity the same as another CPU hog
> > and confirming that each one gets 50%).
> >
> > It appears to be calling i915_gem_inactive_shrink in a loop.  I have
> > probes on entry and return of i915_gem_inactive_shrink and on return
> > of shrink_slab.  I see:
> >
> >          kswapd0    47 [000] 59599.956573: mm_vmscan_kswapd_wake: nid=0 order=0
> >          kswapd0    47 [000] 59599.956575: shrink_zone:
> > (ffffffff810c848c) priority=12 zone=ffff8801005fe000
> >          kswapd0    47 [000] 59599.956576: shrink_zone_return:
> > (ffffffff810c848c <- ffffffff810c96c6) arg1=0
> >          kswapd0    47 [000] 59599.956578: i915_gem_inactive_shrink:

A similar trace came up a bunch of times in Jejb's NMI softlockup/kswapd
consumes the machine thread.  That one was tracked down to slub high
order allocations.

I'm sure that one is burned in on Mel's memory, but after a while the
individual traces fell out of the thread, and I'm not sure the i915 part
stuck out.

-chris

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