[PATCH v2 2/4] drm/msm: Avoid mutex in shrinker_count()

Rob Clark
2021-04-01T01:24:36Z

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>
Tested-by: Douglas Anderson <dianders@chromium.org>
---
drivers/gpu/drm/msm/msm_drv.c | 1 +
drivers/gpu/drm/msm/msm_drv.h | 6 ++-
drivers/gpu/drm/msm/msm_gem.c | 20 ++++++++--
drivers/gpu/drm/msm/msm_gem.h | 53 ++++++++++++++++++++++++--
drivers/gpu/drm/msm/msm_gem_shrinker.c | 28 ++++++--------
5 files changed, 81 insertions(+), 27 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..503168817e24 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -179,8 +179,8 @@ struct msm_drm_private {
* inactive lists (depending on whether or not it is shrinkable) or
* gpu->active_list (for the gpu it is active on[1])
*
- * These lists are protected by mm_lock. If struct_mutex is involved, it
- * should be aquired prior to mm_lock. One should *not* hold mm_lock in
+ * These lists are protected by mm_lock (which should be acquired
+ * before per GEM object lock). One should *not* hold mm_lock in
* get_pages()/vmap()/etc paths, as they can trigger the shrinker.
*
* [1] if someone ever added support for the old 2d cores, there could be
@@ -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 */
+ long 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..bec01bb48fce 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);
@@ -790,10 +791,11 @@ 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);
- list_del_init(&msm_obj->mm_list);
+ list_del(&msm_obj->mm_list);
list_add_tail(&msm_obj->mm_list, &gpu->active_list);
mutex_unlock(&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);

- list_del_init(&msm_obj->mm_list);
- if (msm_obj->madv == MSM_MADV_WILLNEED)
+ if (msm_obj->dontneed)
+ mark_unpurgable(msm_obj);
+
+ list_del(&msm_obj->mm_list);
+ 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..13aabfe92dac 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -50,18 +50,24 @@ 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
*/
uint8_t vmap_count;

- /* And object is either:
- * inactive - on priv->inactive_list
+ /**
+ * An object is either:
+ * inactive - on priv->inactive_dontneed/willneed/purged depending
+ * on status
* active - on one one of the gpu's active_list.. well, at
* least for now we don't have (I don't think) hw sync between
* 2d and 3d one devices which have both, meaning we need to
* block on submit if a bo is already on other ring
- *
*/
struct list_head mm_list;

@@ -186,10 +192,16 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
return msm_obj->active_count;
}

+/* imported/exported objects are not purgable: */
+static inline bool is_unpurgable(struct msm_gem_object *msm_obj)
+{
+ return msm_obj->base.dma_buf && msm_obj->base.import_attach;
+}
+
static inline bool is_purgeable(struct msm_gem_object *msm_obj)
{
return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
- !msm_obj->base.dma_buf && !msm_obj->base.import_attach;
+ !is_unpurgable(msm_obj);
}

static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
@@ -198,6 +210,39 @@ 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 (is_unpurgable(msm_obj))
+ return;
+
+ 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 (is_unpurgable(msm_obj))
+ return;
+
+ 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..f3e948af01c5 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
@@ -45,6 +30,9 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
list_for_each_entry(msm_obj, &priv->inactive_dontneed, mm_list) {
if (freed >= sc->nr_to_scan)
break;
+ /* Use trylock, because we cannot block on a obj that
+ * might be trying to acquire mm_lock
+ */
if (!msm_gem_trylock(&msm_obj->base))
continue;
if (is_purgeable(msm_obj)) {
@@ -56,8 +44,11 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)

mutex_unlock(&priv->mm_lock);

- if (freed > 0)
+ if (freed > 0) {
trace_msm_gem_purge(freed << PAGE_SHIFT);
+ } else {
+ return SHRINK_STOP;
+ }

return freed;
}
@@ -75,6 +66,9 @@ vmap_shrink(struct list_head *mm_list)
unsigned unmapped = 0;

list_for_each_entry(msm_obj, mm_list, mm_list) {
+ /* Use trylock, because we cannot block on a obj that
+ * might be trying to acquire mm_lock
+ */
if (!msm_gem_trylock(&msm_obj->base))
continue;
if (is_vunmapable(msm_obj)) {
--
2.30.2