Re: [PATCH] mm: Throttle shrinkers harder

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Apr 18, 2014 at 12:14:16PM -0700, Andrew Morton wrote:
> On Thu, 10 Apr 2014 08:05:06 +0100 Chris Wilson <chris@chris-wilson.co.uk> wrote:
> 
> > During testing of i915.ko with working texture sets larger than RAM, we
> > encounter OOM with plenty of memory still trapped within writeback, e.g:
> > 
> > [   42.386039] active_anon:10134 inactive_anon:1900781 isolated_anon:32
> >  active_file:33 inactive_file:39 isolated_file:0
> >  unevictable:0 dirty:0 writeback:337627 unstable:0
> >  free:11985 slab_reclaimable:9458 slab_unreclaimable:23614
> >  mapped:41 shmem:1560769 pagetables:1276 bounce:0
> > 
> > If we throttle for writeback following shrink_slab, this gives us time
> > to wait upon the writeback generated by the i915.ko shinker:
> > 
> > [ 4756.750808] active_anon:24386 inactive_anon:900793 isolated_anon:0
> >  active_file:23 inactive_file:20 isolated_file:0
> >  unevictable:0 dirty:0 writeback:0 unstable:0
> >  free:5550 slab_reclaimable:5184 slab_unreclaimable:4888
> >  mapped:3 shmem:472393 pagetables:1249 bounce:0
> > 
> > (Sadly though the test is still failing.)
> > 
> > Testcase: igt/gem_tiled_swapping
> > References: https://bugs.freedesktop.org/show_bug.cgi?id=72742
> 
> i915_gem_object_get_pages_gtt() makes my head spin, but
> https://bugs.freedesktop.org/attachment.cgi?id=90818 says
> "gfp_mask=0x201da" which is 
> 
> ___GFP_HARDWALL|___GFP_COLD|___GFP_FS|___GFP_IO|___GFP_WAIT|___GFP_MOVABLE|___GFP_HIGHMEM
> 
> so this allocation should work and it very bad if the page allocator is
> declaring oom while there is so much writeback in flight, assuming the
> writeback is to eligible zones.

For more head spinning look at the lock stealing dance we do in our
shrinker callbacks i915_gem_inactive_scan|count(). It's not pretty at all,
but it helps to avoids the dreaded oom in a few more cases. Some review of
our mess of ducttape from -mm developers with actual clue would be really
appreciated ...
-Daniel
 
> Mel, Johannes: could you take a look please?
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch