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 <[email protected]>
---
drivers/gpu/drm/ttm/ttm_pool.c | 15 +++++++++++++++
include/linux/shrinker.h | 2 --
mm/shrinker.c | 15 ---------------
3 files changed, 15 insertions(+), 17 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index e1eb73d0b72a..8a35fd48ec46 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 e464b4e9be0e..23ea9360c5d8 100644
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -105,8 +105,6 @@ void shrinker_free_non_registered(struct shrinker *shrinker);
void shrinker_register(struct shrinker *shrinker);
void shrinker_unregister(struct shrinker *shrinker);
-extern void synchronize_shrinkers(void);
-
#ifdef CONFIG_SHRINKER_DEBUG
extern int shrinker_debugfs_add(struct shrinker *shrinker);
extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
diff --git a/mm/shrinker.c b/mm/shrinker.c
index 2f3635ad1b45..3c4d3fe2fa17 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c
@@ -660,18 +660,3 @@ void shrinker_unregister(struct shrinker *shrinker)
kfree(shrinker);
}
EXPORT_SYMBOL(shrinker_unregister);
-
-/**
- * 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);
--
2.30.2
> On Jul 24, 2023, at 17:43, Qi Zheng <[email protected]> wrote:
>
> 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 <[email protected]>
Reviewed-by: Muchun Song <[email protected]>