[PATCH 2/4] drm/msm: Avoid mutex in shrinker_count()

Rob Clark
2021-03-31T22:14:12Z

From: Rob Clark <robdclark@chromium.org>

When the system is under heavy memory pressure, we can end up with lots
of concurrent calls into the shrinker. Keeping a running tab on what we
can shrink avoids grabbing a lock in shrinker->count(), and avoids
shrinker->scan() getting called when not profitable.

Also, we can keep purged objects in their own list to avoid re-traversing
them to help cut down time in the critical section further.

Signed-off-by: Rob Clark <robdclark@chromium.org>
---
drivers/gpu/drm/msm/msm_drv.c | 1 +
drivers/gpu/drm/msm/msm_drv.h | 2 ++
drivers/gpu/drm/msm/msm_gem.c | 16 +++++++++++--
drivers/gpu/drm/msm/msm_gem.h | 32 ++++++++++++++++++++++++++
drivers/gpu/drm/msm/msm_gem_shrinker.c | 17 +-------------
5 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 4f9fa0189a07..3462b0ea14c6 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -476,6 +476,7 @@ static int msm_drm_init(struct device *dev, const struct drm_driver *drv)

INIT_LIST_HEAD(&priv->inactive_willneed);
INIT_LIST_HEAD(&priv->inactive_dontneed);
+ INIT_LIST_HEAD(&priv->inactive_purged);
mutex_init(&priv->mm_lock);

/* Teach lockdep about lock ordering wrt. shrinker: */
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index a1264cfcac5e..3ead5755f695 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -188,6 +188,8 @@ struct msm_drm_private {
*/
struct list_head inactive_willneed; /* inactive + !shrinkable */
struct list_head inactive_dontneed; /* inactive + shrinkable */
+ struct list_head inactive_purged; /* inactive + purged */
+ int shrinkable_count; /* write access under mm_lock */
struct mutex mm_lock;

struct workqueue_struct *wq;
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 9d10739c4eb2..74a92eedc992 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -719,6 +719,7 @@ void msm_gem_purge(struct drm_gem_object *obj)
put_iova_vmas(obj);

msm_obj->madv = __MSM_MADV_PURGED;
+ mark_unpurgable(msm_obj);

drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
drm_gem_free_mmap_offset(obj);
@@ -790,6 +791,7 @@ void msm_gem_active_get(struct drm_gem_object *obj, struct msm_gpu *gpu)
might_sleep();
WARN_ON(!msm_gem_is_locked(obj));
WARN_ON(msm_obj->madv != MSM_MADV_WILLNEED);
+ WARN_ON(msm_obj->dontneed);

if (msm_obj->active_count++ == 0) {
mutex_lock(&priv->mm_lock);
@@ -818,11 +820,19 @@ static void update_inactive(struct msm_gem_object *msm_obj)
mutex_lock(&priv->mm_lock);
WARN_ON(msm_obj->active_count != 0);

+ if (msm_obj->dontneed)
+ mark_unpurgable(msm_obj);
+
list_del_init(&msm_obj->mm_list);
- if (msm_obj->madv == MSM_MADV_WILLNEED)
+ if (msm_obj->madv == MSM_MADV_WILLNEED) {
list_add_tail(&msm_obj->mm_list, &priv->inactive_willneed);
- else
+ } else if (msm_obj->madv == MSM_MADV_DONTNEED) {
list_add_tail(&msm_obj->mm_list, &priv->inactive_dontneed);
+ mark_purgable(msm_obj);
+ } else {
+ WARN_ON(msm_obj->madv != __MSM_MADV_PURGED);
+ list_add_tail(&msm_obj->mm_list, &priv->inactive_purged);
+ }

mutex_unlock(&priv->mm_lock);
}
@@ -971,6 +981,8 @@ void msm_gem_free_object(struct drm_gem_object *obj)
struct msm_drm_private *priv = dev->dev_private;

mutex_lock(&priv->mm_lock);
+ if (msm_obj->dontneed)
+ mark_unpurgable(msm_obj);
list_del(&msm_obj->mm_list);
mutex_unlock(&priv->mm_lock);

diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index 7a9107cf1818..0feabae75d3d 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -50,6 +50,11 @@ struct msm_gem_object {
*/
uint8_t madv;

+ /**
+ * Is object on inactive_dontneed list (ie. counted in priv->shrinkable_count)?
+ */
+ bool dontneed : 1;
+
/**
* count of active vmap'ing
*/
@@ -198,6 +203,33 @@ static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
}

+static inline void mark_purgable(struct msm_gem_object *msm_obj)
+{
+ struct msm_drm_private *priv = msm_obj->base.dev->dev_private;
+
+ WARN_ON(!mutex_is_locked(&priv->mm_lock));
+
+ if (WARN_ON(msm_obj->dontneed))
+ return;
+
+ priv->shrinkable_count += msm_obj->base.size >> PAGE_SHIFT;
+ msm_obj->dontneed = true;
+}
+
+static inline void mark_unpurgable(struct msm_gem_object *msm_obj)
+{
+ struct msm_drm_private *priv = msm_obj->base.dev->dev_private;
+
+ WARN_ON(!mutex_is_locked(&priv->mm_lock));
+
+ if (WARN_ON(!msm_obj->dontneed))
+ return;
+
+ priv->shrinkable_count -= msm_obj->base.size >> PAGE_SHIFT;
+ WARN_ON(priv->shrinkable_count < 0);
+ msm_obj->dontneed = false;
+}
+
void msm_gem_purge(struct drm_gem_object *obj);
void msm_gem_vunmap(struct drm_gem_object *obj);

diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index 9d5248be746f..7db8375f2430 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -14,22 +14,7 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
{
struct msm_drm_private *priv =
container_of(shrinker, struct msm_drm_private, shrinker);
- struct msm_gem_object *msm_obj;
- unsigned long count = 0;
-
- mutex_lock(&priv->mm_lock);
-
- list_for_each_entry(msm_obj, &priv->inactive_dontneed, mm_list) {
- if (!msm_gem_trylock(&msm_obj->base))
- continue;
- if (is_purgeable(msm_obj))
- count += msm_obj->base.size >> PAGE_SHIFT;
- msm_gem_unlock(&msm_obj->base);
- }
-
- mutex_unlock(&priv->mm_lock);
-
- return count;
+ return priv->shrinkable_count;
}

static unsigned long
--
2.30.2