Re: Paging out when free memory is low but not exhausted (and available memory remains high)

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[Let's CC i915 people - the email thread started here:
http://lkml.kernel.org/r/e994b0a76099437b8edbae925e9ccac8@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Long story short, there is a swap out activity even when there is a
clean page cache available that could be reclaimed and there is a
suspicion that the i915 shrinker might be involved. Could you guys have
a look please?]

On Sun 02-02-20 22:56:56, Chris Edwards wrote:
> ________________________________________
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Sent: Thursday, 30 January 2020 05:39
> 
> > Chris, could you trace the i915 shrinker?
> > 
> > Enable the shrinker trace point:
> > 
> > # echo 1 >/sys/kernel/debug/tracing/events/i915/i915_gem_shrink/enable
> > 
> > Then watch for events while the swapping is occuring:
> > 
> > # cat /sys/kernel/debug/tracing/trace
> 
> ________________________________________
> 
> Thanks Johannes - that seems to confirm your suspicion: the kernel trace has a lot of contiguous entries relating to kswapd and the i915 shrinker:
> 
>          kswapd0-90    [001] .... 251812.619380: i915_gem_shrink: dev=0, target=243, flags=17
>          kswapd0-90    [001] .... 251813.194977: i915_gem_shrink: dev=0, target=496, flags=3
>          kswapd0-90    [001] .... 251813.196205: i915_gem_shrink: dev=0, target=850, flags=3
>          kswapd0-90    [001] .... 251813.196207: i915_gem_shrink: dev=0, target=808, flags=17
>          kswapd0-90    [001] .... 251813.399428: i915_gem_shrink: dev=0, target=470, flags=3
>          kswapd0-90    [001] .... 251813.429971: i915_gem_shrink: dev=0, target=666, flags=3
>          kswapd0-90    [001] .... 251813.430039: i915_gem_shrink: dev=0, target=259, flags=17
>          kswapd0-90    [001] .... 251813.905045: i915_gem_shrink: dev=0, target=573, flags=3
>          kswapd0-90    [001] .... 251813.905085: i915_gem_shrink: dev=0, target=174, flags=17
>          kswapd0-90    [001] .N.. 251813.945542: i915_gem_shrink: dev=0, target=670, flags=3
>          kswapd0-90    [001] .... 251813.945569: i915_gem_shrink: dev=0, target=474, flags=17
>          kswapd0-90    [001] .... 251814.734973: i915_gem_shrink: dev=0, target=611, flags=3
>          kswapd0-90    [001] .... 251814.735024: i915_gem_shrink: dev=0, target=417, flags=17
>          kswapd0-90    [001] .... 251814.807983: i915_gem_shrink: dev=0, target=990, flags=3
>          kswapd0-90    [001] .... 251814.807998: i915_gem_shrink: dev=0, target=962, flags=17
>          kswapd0-90    [000] .... 251815.146950: i915_gem_shrink: dev=0, target=860, flags=3
>          kswapd0-90    [000] .... 251815.146970: i915_gem_shrink: dev=0, target=758, flags=17
>          kswapd0-90    [000] .... 251815.257367: i915_gem_shrink: dev=0, target=924, flags=3
>          kswapd0-90    [000] .... 251815.257384: i915_gem_shrink: dev=0, target=832, flags=17
>          kswapd0-90    [000] .... 251816.036147: i915_gem_shrink: dev=0, target=576, flags=3
>          kswapd0-90    [000] .... 251816.036166: i915_gem_shrink: dev=0, target=140, flags=17
>          kswapd0-90    [000] .... 251816.123591: i915_gem_shrink: dev=0, target=403, flags=3
>          kswapd0-90    [000] .... 251816.124549: i915_gem_shrink: dev=0, target=546, flags=3
>          kswapd0-90    [000] .... 251816.125415: i915_gem_shrink: dev=0, target=546, flags=3
>          kswapd0-90    [000] .... 251816.126478: i915_gem_shrink: dev=0, target=546, flags=3
>          kswapd0-90    [000] .... 251816.127380: i915_gem_shrink: dev=0, target=542, flags=3
>          kswapd0-90    [000] .... 251816.128163: i915_gem_shrink: dev=0, target=522, flags=3
>          kswapd0-90    [000] .... 251816.128748: i915_gem_shrink: dev=0, target=522, flags=3
>          kswapd0-90    [000] .... 251816.129303: i915_gem_shrink: dev=0, target=522, flags=3
>          kswapd0-90    [000] .... 251816.131522: i915_gem_shrink: dev=0, target=522, flags=3
>          kswapd0-90    [000] .... 251816.133711: i915_gem_shrink: dev=0, target=522, flags=3
>          kswapd0-90    [000] .... 251816.134317: i915_gem_shrink: dev=0, target=568, flags=3
>          kswapd0-90    [000] .... 251816.134849: i915_gem_shrink: dev=0, target=568, flags=3
>          kswapd0-90    [000] .... 251816.135647: i915_gem_shrink: dev=0, target=568, flags=3
>          kswapd0-90    [000] .... 251816.233664: i915_gem_shrink: dev=0, target=483, flags=3
>          kswapd0-90    [000] .... 251816.234041: i915_gem_shrink: dev=0, target=858, flags=3
>          kswapd0-90    [000] .... 251816.234060: i915_gem_shrink: dev=0, target=612, flags=17
>          kswapd0-90    [000] .... 251816.818646: i915_gem_shrink: dev=0, target=654, flags=3
>          kswapd0-90    [000] .... 251816.818702: i915_gem_shrink: dev=0, target=400, flags=17
>          kswapd0-90    [000] .... 251816.865547: i915_gem_shrink: dev=0, target=676, flags=3
>          kswapd0-90    [000] .... 251816.865570: i915_gem_shrink: dev=0, target=499, flags=17
>          kswapd0-90    [000] .... 251817.299401: i915_gem_shrink: dev=0, target=556, flags=3
>          kswapd0-90    [000] .... 251817.299435: i915_gem_shrink: dev=0, target=355, flags=17
>          kswapd0-90    [000] .... 251817.301099: i915_gem_shrink: dev=0, target=566, flags=3
>          kswapd0-90    [000] .... 251817.301112: i915_gem_shrink: dev=0, target=512, flags=17
>          kswapd0-90    [000] .... 251817.369283: i915_gem_shrink: dev=0, target=749, flags=3
>          kswapd0-90    [000] .... 251817.369385: i915_gem_shrink: dev=0, target=115, flags=17
>          kswapd0-90    [000] .... 251817.911052: i915_gem_shrink: dev=0, target=605, flags=3
>          kswapd0-90    [000] .... 251817.911080: i915_gem_shrink: dev=0, target=474, flags=17
>          kswapd0-90    [000] .... 251817.964954: i915_gem_shrink: dev=0, target=709, flags=3
>          kswapd0-90    [000] .... 251817.964973: i915_gem_shrink: dev=0, target=589, flags=17
>          kswapd0-90    [001] .... 251819.005872: i915_gem_shrink: dev=0, target=490, flags=3
> 
> Thanks - and Michal, I hope you had a nice holiday. :)
> --
> Chris

-- 
Michal Hocko
SUSE Labs
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