[PATCH v4 30/48] vmw_balloon: dynamically allocate the vmw-balloon shrinker

[Qi Zheng via Linux-erofs]

In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the vmw-balloon shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct vmballoon.

And we can simply exit vmballoon_init() when registering the shrinker
fails. So the shrinker_registered indication is redundant, just remove it.

Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com>
Reviewed-by: Muchun Song <songmuc...@bytedance.com>
---
 drivers/misc/vmw_balloon.c | 38 ++++++++++++--------------------------
 1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
index 9ce9b9e0e9b6..ac2cdb6cdf74 100644
--- a/drivers/misc/vmw_balloon.c
+++ b/drivers/misc/vmw_balloon.c
@@ -380,16 +380,7 @@ struct vmballoon {
        /**
         * @shrinker: shrinker interface that is used to avoid over-inflation.
         */
-       struct shrinker shrinker;
-
-       /**
-        * @shrinker_registered: whether the shrinker was registered.
-        *
-        * The shrinker interface does not handle gracefully the removal of
-        * shrinker that was not registered before. This indication allows to
-        * simplify the unregistration process.
-        */
-       bool shrinker_registered;
+       struct shrinker *shrinker;
 };
 
 static struct vmballoon balloon;
@@ -1568,29 +1559,27 @@ static unsigned long vmballoon_shrinker_count(struct 
shrinker *shrinker,
 
 static void vmballoon_unregister_shrinker(struct vmballoon *b)
 {
-       if (b->shrinker_registered)
-               unregister_shrinker(&b->shrinker);
-       b->shrinker_registered = false;
+       shrinker_free(b->shrinker);
 }
 
 static int vmballoon_register_shrinker(struct vmballoon *b)
 {
-       int r;
-
        /* Do nothing if the shrinker is not enabled */
        if (!vmwballoon_shrinker_enable)
                return 0;
 
-       b->shrinker.scan_objects = vmballoon_shrinker_scan;
-       b->shrinker.count_objects = vmballoon_shrinker_count;
-       b->shrinker.seeks = DEFAULT_SEEKS;
+       b->shrinker = shrinker_alloc(0, "vmw-balloon");
+       if (!b->shrinker)
+               return -ENOMEM;
 
-       r = register_shrinker(&b->shrinker, "vmw-balloon");
+       b->shrinker->scan_objects = vmballoon_shrinker_scan;
+       b->shrinker->count_objects = vmballoon_shrinker_count;
+       b->shrinker->seeks = DEFAULT_SEEKS;
+       b->shrinker->private_data = b;
 
-       if (r == 0)
-               b->shrinker_registered = true;
+       shrinker_register(b->shrinker);
 
-       return r;
+       return 0;
 }
 
 /*
@@ -1883,7 +1872,7 @@ static int __init vmballoon_init(void)
 
        error = vmballoon_register_shrinker(&balloon);
        if (error)
-               goto fail;
+               return error;
 
        /*
         * Initialization of compaction must be done after the call to
@@ -1905,9 +1894,6 @@ static int __init vmballoon_init(void)
        vmballoon_debugfs_init(&balloon);
 
        return 0;
-fail:
-       vmballoon_unregister_shrinker(&balloon);
-       return error;
 }
 
 /*
-- 
2.30.2