Re: [PATCH 0/8] drm/msm: Swappable GEM objects

[Daniel Vetter]

On Mon, Apr 05, 2021 at 10:45:23AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@xxxxxxxxxxxx>
> 
> One would normally hope not to be under enough memory pressure to need
> to swap GEM objects to disk backed swap.  But memory backed zram swap
> (as enabled on chromebooks, for example) can actually be quite fast
> and useful on devices with less RAM.  On a 4GB device, opening up ~4
> memory intensive web pages (in separate windows rather than tabs, to try
> and prevent tab discard), I see ~500MB worth of GEM objects, of which
> maybe only 10% are active at any time, and with unpin/evict enabled,
> only about half resident (which is a number that gets much lower if you
> simulate extreme memory pressure).  Assuming a 2:1 compression ratio (I
> see a bit higher in practice, but cannot isolate swapped out GEM pages
> vs other), that is like having an extra 100+MB of RAM, or more under
> higher memory pressure.
> 
> Rob Clark (8):
>   drm/msm: ratelimit GEM related WARN_ON()s
>   drm/msm: Reorganize msm_gem_shrinker_scan()
>   drm/msm: Clear msm_obj->sgt in put_pages()
>   drm/msm: Split iova purge and close
>   drm/msm: Add $debugfs/gem stats on resident objects
>   drm/msm: Track potentially evictable objects
>   drm/msm: Small msm_gem_purge() fix
>   drm/msm: Support evicting GEM objects to swap

Given how much entertainement shrinkers are, should we aim for more common
code here?

Christian has tons of fun with adding something like this for ttm (well
different shades of grey). i915 is going to adopt ttm, at least for
discrete.

The locking is also an utter pain, and msm seems to still live a lot in
its own land here. I think as much as possible a standard approach here
would be really good, ideally maybe as building blocks shared between ttm
and gem-shmem drivers ...
-Daniel

> 
>  drivers/gpu/drm/msm/msm_drv.c          |   2 +-
>  drivers/gpu/drm/msm/msm_drv.h          |  13 ++-
>  drivers/gpu/drm/msm/msm_gem.c          | 155 +++++++++++++++++--------
>  drivers/gpu/drm/msm/msm_gem.h          |  68 +++++++++--
>  drivers/gpu/drm/msm/msm_gem_shrinker.c | 129 ++++++++++++--------
>  drivers/gpu/drm/msm/msm_gpu_trace.h    |  13 +++
>  6 files changed, 272 insertions(+), 108 deletions(-)
> 
> -- 
> 2.30.2
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch