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

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Mon, 2011-06-27 at 12:03 +0100, Mel Gorman wrote:
> On Fri, Jun 24, 2011 at 02:54:11PM -0400, Chris Mason wrote:
> > 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.
> > 
> 
> I expect that Jejb's lockup is also fixed by "Stop kswapd consuming
> 100% CPU when highest zone is small". i915 didn't help but at the end
> of the day, kswapd shouldn't have been shrinking slab so aggressively.

It will be a while before I can try this out, I'm afraid ... the laptop
is currently on tour in Europe with its owner.  I finally just
downgraded it to FC13 which made most of the issues go away.

James



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