[PATCH v3 2/3] mm: kmemleak: Simple memory allocation pool for kmemleak objects

[Catalin Marinas]

Add a memory pool for struct kmemleak_object in case the normal
kmem_cache_alloc() fails under the gfp constraints passed by the caller.
The mem_pool[] array size is currently fixed at 16000.

Signed-off-by: Catalin Marinas <catalin.mari...@arm.com>
---
 mm/kmemleak.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 52 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 5ba7fad00fda..2fb86524d70b 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -180,11 +180,17 @@ struct kmemleak_object {
 #define HEX_ASCII              1
 /* max number of lines to be printed */
 #define HEX_MAX_LINES          2
+/* memory pool size */
+#define MEM_POOL_SIZE          16000
 
 /* the list of all allocated objects */
 static LIST_HEAD(object_list);
 /* the list of gray-colored objects (see color_gray comment below) */
 static LIST_HEAD(gray_list);
+/* memory pool allocation */
+static struct kmemleak_object mem_pool[MEM_POOL_SIZE];
+static int mem_pool_free_count = ARRAY_SIZE(mem_pool);
+static LIST_HEAD(mem_pool_free_list);
 /* search tree for object boundaries */
 static struct rb_root object_tree_root = RB_ROOT;
 /* rw_lock protecting the access to object_list and object_tree_root */
@@ -451,6 +457,50 @@ static int get_object(struct kmemleak_object *object)
        return atomic_inc_not_zero(&object->use_count);
 }
 
+/*
+ * Memory pool allocation and freeing. kmemleak_lock must not be held.
+ */
+static struct kmemleak_object *mem_pool_alloc(gfp_t gfp)
+{
+       unsigned long flags;
+       struct kmemleak_object *object;
+
+       /* try the slab allocator first */
+       object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp));
+       if (object)
+               return object;
+
+       /* slab allocation failed, try the memory pool */
+       write_lock_irqsave(&kmemleak_lock, flags);
+       object = list_first_entry_or_null(&mem_pool_free_list,
+                                         typeof(*object), object_list);
+       if (object)
+               list_del(&object->object_list);
+       else if (mem_pool_free_count)
+               object = &mem_pool[--mem_pool_free_count];
+       write_unlock_irqrestore(&kmemleak_lock, flags);
+
+       return object;
+}
+
+/*
+ * Return the object to either the slab allocator or the memory pool.
+ */
+static void mem_pool_free(struct kmemleak_object *object)
+{
+       unsigned long flags;
+
+       if (object < mem_pool || object >= mem_pool + ARRAY_SIZE(mem_pool)) {
+               kmem_cache_free(object_cache, object);
+               return;
+       }
+
+       /* add the object to the memory pool free list */
+       write_lock_irqsave(&kmemleak_lock, flags);
+       list_add(&object->object_list, &mem_pool_free_list);
+       write_unlock_irqrestore(&kmemleak_lock, flags);
+}
+
 /*
  * RCU callback to free a kmemleak_object.
  */
@@ -469,7 +519,7 @@ static void free_object_rcu(struct rcu_head *rcu)
                hlist_del(&area->node);
                kmem_cache_free(scan_area_cache, area);
        }
-       kmem_cache_free(object_cache, object);
+       mem_pool_free(object);
 }
 
 /*
@@ -552,7 +602,7 @@ static struct kmemleak_object *create_object(unsigned long 
ptr, size_t size,
        struct rb_node **link, *rb_parent;
        unsigned long untagged_ptr;
 
-       object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp));
+       object = mem_pool_alloc(gfp);
        if (!object) {
                pr_warn("Cannot allocate a kmemleak_object structure\n");
                kmemleak_disable();