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

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Andrew Lutomirski <luto@xxxxxxx> 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:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956589: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=320
>          kswapd0    47 [000] 59599.956589: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956592: i915_gem_inactive_shrink:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956602: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=320
>          kswapd0    47 [000] 59599.956603: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956605: shrink_zone:
> (ffffffff810c848c) priority=12 zone=ffff8801005fee00
>          kswapd0    47 [000] 59599.956606: shrink_zone_return:
> (ffffffff810c848c <- ffffffff810c96c6) arg1=0
>          kswapd0    47 [000] 59599.956608: i915_gem_inactive_shrink:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956609: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=0
>          kswapd0    47 [000] 59599.956610: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956611: mm_vmscan_kswapd_wake: nid=0 order=0
>          kswapd0    47 [000] 59599.956612: shrink_zone:
> (ffffffff810c848c) priority=12 zone=ffff8801005fe000
>          kswapd0    47 [000] 59599.956614: shrink_zone_return:
> (ffffffff810c848c <- ffffffff810c96c6) arg1=0
>          kswapd0    47 [000] 59599.956616: i915_gem_inactive_shrink:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956617: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=0
>          kswapd0    47 [000] 59599.956618: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956620: i915_gem_inactive_shrink:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956621: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=0
>          kswapd0    47 [000] 59599.956621: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956623: shrink_zone:
> (ffffffff810c848c) priority=12 zone=ffff8801005fee00
>          kswapd0    47 [000] 59599.956624: shrink_zone_return:
> (ffffffff810c848c <- ffffffff810c96c6) arg1=0
>          kswapd0    47 [000] 59599.956626: i915_gem_inactive_shrink:
> (ffffffffa0081e48) gfp_mask=d0 nr_to_scan=0
>          kswapd0    47 [000] 59599.956627: shrink_return:
> (ffffffffa0081e48 <- ffffffff810c6a62) arg1=0
>          kswapd0    47 [000] 59599.956628: shrink_slab_return:
> (ffffffff810c69f5 <- ffffffff810c96ec) arg1=0
>          kswapd0    47 [000] 59599.956629: mm_vmscan_kswapd_wake: nid=0 order=0
>
> The command was:
>
> perf record -g -aR -p 47 -e probe:i915_gem_inactive_shrink -e
> probe:shrink_return -e probe:shrink_slab_return -e probe:shrink_zone
> -e probe:shrink_zone_return -e probe:kswapd_try_to_sleep -e
> vmscan:mm_vmscan_kswapd_sleep -e vmscan:mm_vmscan_kswapd_wake -e
> vmscan:mm_vmscan_wakeup_kswapd -e vmscan:mm_vmscan_lru_shrink_inactive
> -e probe:wakeup_kswapd; perf script
>
> (shrink_return is i915_gem_inactive_shrink's return.  sorry, badly named.)
>
> It looks like something kswapd_try_to_sleep is not getting called.
>
> I do not know how to reproduce this, but I'll leave it running overnight.
>
> --Andy
>
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-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only

--
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