APPLIED: [PATCH][SRU][F] UBUNTU: SAUCE: drm/i915: prevent direct writeback from the shrinker

[Andrea Righi]

On Mon, Apr 20, 2020 at 04:19:03PM +0200, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1861359
> 
> The i915 shrinker can make the system unresponsive and kill interactive
> performance by swapping out dirty objects to reclaim more memory.
> 
> Avoid the lags by preventing to swap out dirty objects from any task
> (except kswapd).
> 
> This is not required in 5.5+, because it is properly fixed by commit
> 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")
> 
> However, backporting this commit to 5.4 is not trivial and the
> regression potential is high. A simple change like this can be a
> reasonable compromise to prevent the problem and avoid the risk of
> introducing other bugs.
> 
> Fixes: 2d6692e642e7 ("drm/i915: Start writeback from the shrinker")
> Signed-off-by: Sultan Alsawaf <sultan.alsawaf at canonical.com>
> Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> index edd21d14e64f..793bd586b80b 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> @@ -357,8 +357,7 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
>  				sc->nr_to_scan,
>  				&sc->nr_scanned,
>  				I915_SHRINK_BOUND |
> -				I915_SHRINK_UNBOUND |
> -				I915_SHRINK_WRITEBACK);
> +				I915_SHRINK_UNBOUND);
>  	if (sc->nr_scanned < sc->nr_to_scan && current_is_kswapd()) {
>  		intel_wakeref_t wakeref;
>  
> -- 
> 2.25.1
>