Re: [PATCH v2 29/47] vmw_balloon: dynamically allocate the vmw-balloon shrinker

[Muchun Song]

> On Jul 24, 2023, at 17:43, Qi Zheng  wrote:
> 
> 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 

Nice cleanup.

Reviewed-by: Muchun Song 

[PATCH v2 29/47] vmw_balloon: dynamically allocate the vmw-balloon shrinker

[Qi Zheng]

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 
---
 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..d216d4dc042e 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(>shrinker);
-   b->shrinker_registered = false;
+   shrinker_unregister(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(>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();
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();
 
return 0;
-fail:
-   vmballoon_unregister_shrinker();
-   return error;
 }
 
 /*
-- 
2.30.2