[PATCH 22/29] drm/ttm: introduce pool_shrink_rwsem

Qi Zheng
2023-06-22T09:03:31Z

Currently, the synchronize_shrinkers() is only used by TTM
pool. It only requires that no shrinkers run in parallel.

After we use RCU+refcount method to implement the lockless
slab shrink, we can not use shrinker_rwsem or synchronize_rcu()
to guarantee that all shrinker invocations have seen an update
before freeing memory.

So we introduce a new pool_shrink_rwsem to implement a private
synchronize_shrinkers(), so as to achieve the same purpose.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
drivers/gpu/drm/ttm/ttm_pool.c | 15 +++++++++++++++
include/linux/shrinker.h | 1 -
mm/vmscan.c | 15 ---------------
3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index cddb9151d20f..713b1c0a70e1 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -74,6 +74,7 @@ static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
static spinlock_t shrinker_lock;
static struct list_head shrinker_list;
static struct shrinker mm_shrinker;
+static DECLARE_RWSEM(pool_shrink_rwsem);

/* Allocate pages of size 1 << order with the given gfp_flags */
static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
@@ -317,6 +318,7 @@ static unsigned int ttm_pool_shrink(void)
unsigned int num_pages;
struct page *p;

+ down_read(&pool_shrink_rwsem);
spin_lock(&shrinker_lock);
pt = list_first_entry(&shrinker_list, typeof(*pt), shrinker_list);
list_move_tail(&pt->shrinker_list, &shrinker_list);
@@ -329,6 +331,7 @@ static unsigned int ttm_pool_shrink(void)
} else {
num_pages = 0;
}
+ up_read(&pool_shrink_rwsem);

return num_pages;
}
@@ -572,6 +575,18 @@ void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
}
EXPORT_SYMBOL(ttm_pool_init);

+/**
+ * synchronize_shrinkers - Wait for all running shrinkers to complete.
+ *
+ * This is useful to guarantee that all shrinker invocations have seen an
+ * update, before freeing memory, similar to rcu.
+ */
+static void synchronize_shrinkers(void)
+{
+ down_write(&pool_shrink_rwsem);
+ up_write(&pool_shrink_rwsem);
+}
+
/**
* ttm_pool_fini - Cleanup a pool
*
diff --git a/include/linux/shrinker.h b/include/linux/shrinker.h
index 8e9ba6fa3fcc..4094e4c44e80 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -105,7 +105,6 @@ extern int __printf(2, 3) register_shrinker(struct shrinker *shrinker,
const char *fmt, ...);
extern void unregister_shrinker(struct shrinker *shrinker);
extern void free_prealloced_shrinker(struct shrinker *shrinker);
-extern void synchronize_shrinkers(void);

typedef unsigned long (*count_objects_cb)(struct shrinker *s,
struct shrink_control *sc);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 64ff598fbad9..3a8d50ad6ff6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -844,21 +844,6 @@ void unregister_and_free_shrinker(struct shrinker *shrinker)
}
EXPORT_SYMBOL(unregister_and_free_shrinker);

-/**
- * synchronize_shrinkers - Wait for all running shrinkers to complete.
- *
- * This is equivalent to calling unregister_shrink() and register_shrinker(),
- * but atomically and with less overhead. This is useful to guarantee that all
- * shrinker invocations have seen an update, before freeing memory, similar to
- * rcu.
- */
-void synchronize_shrinkers(void)
-{
- down_write(&shrinker_rwsem);
- up_write(&shrinker_rwsem);
-}
-EXPORT_SYMBOL(synchronize_shrinkers);
-
#define SHRINK_BATCH 128

static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
--
2.30.2