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Message-ID: <d1c560f1-0201-7b41-bb27-d6bcb332b8d4@suse.de>
Date: Fri, 17 Feb 2023 13:02:05 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Dmitry Osipenko <dmitry.osipenko@...labora.com>,
David Airlie <airlied@...il.com>,
Gerd Hoffmann <kraxel@...hat.com>,
Gurchetan Singh <gurchetansingh@...omium.org>,
Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
Daniel Almeida <daniel.almeida@...labora.com>,
Gustavo Padovan <gustavo.padovan@...labora.com>,
Daniel Stone <daniel@...ishbar.org>,
Tomeu Vizoso <tomeu.vizoso@...labora.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Rob Clark <robdclark@...il.com>,
Sumit Semwal <sumit.semwal@...aro.org>,
Christian König <christian.koenig@....com>,
Qiang Yu <yuq825@...il.com>,
Steven Price <steven.price@....com>,
Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
Rob Herring <robh@...nel.org>, Sean Paul <sean@...rly.run>,
Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v10 01/11] drm/msm/gem: Prevent blocking within shrinker
loop
Hi
Am 08.01.23 um 22:04 schrieb Dmitry Osipenko:
> Consider this scenario:
>
> 1. APP1 continuously creates lots of small GEMs
> 2. APP2 triggers `drop_caches`
> 3. Shrinker starts to evict APP1 GEMs, while APP1 produces new purgeable
> GEMs
> 4. msm_gem_shrinker_scan() returns non-zero number of freed pages
> and causes shrinker to try shrink more
> 5. msm_gem_shrinker_scan() returns non-zero number of freed pages again,
> goto 4
> 6. The APP2 is blocked in `drop_caches` until APP1 stops producing
> purgeable GEMs
>
> To prevent this blocking scenario, check number of remaining pages
> that GPU shrinker couldn't release due to a GEM locking contention
> or shrinking rejection. If there are no remaining pages left to shrink,
> then there is no need to free up more pages and shrinker may break out
> from the loop.
>
> This problem was found during shrinker/madvise IOCTL testing of
> virtio-gpu driver. The MSM driver is affected in the same way.
>
> Reviewed-by: Rob Clark <robdclark@...il.com>
> Fixes: b352ba54a820 ("drm/msm/gem: Convert to using drm_gem_lru")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
> drivers/gpu/drm/drm_gem.c | 9 +++++++--
> drivers/gpu/drm/msm/msm_gem_shrinker.c | 8 ++++++--
> include/drm/drm_gem.h | 4 +++-
> 3 files changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 59a0bb5ebd85..c6bca5ac6e0f 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1388,10 +1388,13 @@ EXPORT_SYMBOL(drm_gem_lru_move_tail);
> *
> * @lru: The LRU to scan
> * @nr_to_scan: The number of pages to try to reclaim
> + * @remaining: The number of pages left to reclaim
> * @shrink: Callback to try to shrink/reclaim the object.
> */
> unsigned long
> -drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
> +drm_gem_lru_scan(struct drm_gem_lru *lru,
> + unsigned int nr_to_scan,
> + unsigned long *remaining,
> bool (*shrink)(struct drm_gem_object *obj))
> {
> struct drm_gem_lru still_in_lru;
> @@ -1430,8 +1433,10 @@ drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
> * hit shrinker in response to trying to get backing pages
> * for this obj (ie. while it's lock is already held)
> */
> - if (!dma_resv_trylock(obj->resv))
> + if (!dma_resv_trylock(obj->resv)) {
> + *remaining += obj->size >> PAGE_SHIFT;
> goto tail;
> + }
>
> if (shrink(obj)) {
> freed += obj->size >> PAGE_SHIFT;
> diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> index 051bdbc093cf..b7c1242014ec 100644
> --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> @@ -116,12 +116,14 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> };
> long nr = sc->nr_to_scan;
> unsigned long freed = 0;
> + unsigned long remaining = 0;
>
> for (unsigned i = 0; (nr > 0) && (i < ARRAY_SIZE(stages)); i++) {
> if (!stages[i].cond)
> continue;
> stages[i].freed =
> - drm_gem_lru_scan(stages[i].lru, nr, stages[i].shrink);
> + drm_gem_lru_scan(stages[i].lru, nr, &remaining,
This function relies in remaining being pre-initialized. That's not
obvious and error prone. At least, pass-in something like
&stages[i].remaining that is then initialized internally by
drm_gem_lru_scan() to zero. And similar to freed, sum up the individual
stages' remaining here.
TBH I somehow don't like the overall design of how all these functions
interact with each other. But I also can't really point to the actual
problem. So it's best to take what you have here; maybe with the change
I proposed.
Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
Best regards
Thomas
> + stages[i].shrink);
> nr -= stages[i].freed;
> freed += stages[i].freed;
> }
> @@ -132,7 +134,7 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> stages[3].freed);
> }
>
> - return (freed > 0) ? freed : SHRINK_STOP;
> + return (freed > 0 && remaining > 0) ? freed : SHRINK_STOP;
> }
>
> #ifdef CONFIG_DEBUG_FS
> @@ -182,10 +184,12 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
> NULL,
> };
> unsigned idx, unmapped = 0;
> + unsigned long remaining = 0;
>
> for (idx = 0; lrus[idx] && unmapped < vmap_shrink_limit; idx++) {
> unmapped += drm_gem_lru_scan(lrus[idx],
> vmap_shrink_limit - unmapped,
> + &remaining,
> vmap_shrink);
> }
>
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 772a4adf5287..f1f00fc2dba6 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -476,7 +476,9 @@ int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
> void drm_gem_lru_init(struct drm_gem_lru *lru, struct mutex *lock);
> void drm_gem_lru_remove(struct drm_gem_object *obj);
> void drm_gem_lru_move_tail(struct drm_gem_lru *lru, struct drm_gem_object *obj);
> -unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru, unsigned nr_to_scan,
> +unsigned long drm_gem_lru_scan(struct drm_gem_lru *lru,
> + unsigned int nr_to_scan,
> + unsigned long *remaining,
> bool (*shrink)(struct drm_gem_object *obj));
>
> #endif /* __DRM_GEM_H__ */
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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