[RFC v1 2/5] mm/slab: Copy main data structures of kvfree_rcu()

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

This patch copies main data structures of kvfree_rcu() API
from the kernel/rcu/tree.c into slab_common.c file. Later on,
it will be removed from the tree.c.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 mm/slab_common.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 893d32059915..a249fdb0d92e 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1338,3 +1338,98 @@ EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
 EXPORT_TRACEPOINT_SYMBOL(kfree);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_free);
 
+/* Maximum number of jiffies to wait before draining a batch. */
+#define KFREE_DRAIN_JIFFIES (5 * HZ)
+#define KFREE_N_BATCHES 2
+#define FREE_N_CHANNELS 2
+
+/**
+ * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
+ * @list: List node. All blocks are linked between each other
+ * @gp_snap: Snapshot of RCU state for objects placed to this bulk
+ * @nr_records: Number of active pointers in the array
+ * @records: Array of the kvfree_rcu() pointers
+ */
+struct kvfree_rcu_bulk_data {
+	struct list_head list;
+	struct rcu_gp_oldstate gp_snap;
+	unsigned long nr_records;
+	void *records[] __counted_by(nr_records);
+};
+
+/*
+ * This macro defines how many entries the "records" array
+ * will contain. It is based on the fact that the size of
+ * kvfree_rcu_bulk_data structure becomes exactly one page.
+ */
+#define KVFREE_BULK_MAX_ENTR \
+	((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
+
+/**
+ * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
+ * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
+ * @head_free: List of kfree_rcu() objects waiting for a grace period
+ * @head_free_gp_snap: Grace-period snapshot to check for attempted premature frees.
+ * @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
+ * @krcp: Pointer to @kfree_rcu_cpu structure
+ */
+
+struct kfree_rcu_cpu_work {
+	struct rcu_work rcu_work;
+	struct rcu_head *head_free;
+	struct rcu_gp_oldstate head_free_gp_snap;
+	struct list_head bulk_head_free[FREE_N_CHANNELS];
+	struct kfree_rcu_cpu *krcp;
+};
+
+/**
+ * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
+ * @head: List of kfree_rcu() objects not yet waiting for a grace period
+ * @head_gp_snap: Snapshot of RCU state for objects placed to "@head"
+ * @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
+ * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
+ * @lock: Synchronize access to this structure
+ * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
+ * @initialized: The @rcu_work fields have been initialized
+ * @head_count: Number of objects in rcu_head singular list
+ * @bulk_count: Number of objects in bulk-list
+ * @bkvcache:
+ *	A simple cache list that contains objects for reuse purpose.
+ *	In order to save some per-cpu space the list is singular.
+ *	Even though it is lockless an access has to be protected by the
+ *	per-cpu lock.
+ * @page_cache_work: A work to refill the cache when it is empty
+ * @backoff_page_cache_fill: Delay cache refills
+ * @work_in_progress: Indicates that page_cache_work is running
+ * @hrtimer: A hrtimer for scheduling a page_cache_work
+ * @nr_bkv_objs: number of allocated objects at @bkvcache.
+ *
+ * This is a per-CPU structure.  The reason that it is not included in
+ * the rcu_data structure is to permit this code to be extracted from
+ * the RCU files.  Such extraction could allow further optimization of
+ * the interactions with the slab allocators.
+ */
+struct kfree_rcu_cpu {
+	// Objects queued on a linked list
+	// through their rcu_head structures.
+	struct rcu_head *head;
+	unsigned long head_gp_snap;
+	atomic_t head_count;
+
+	// Objects queued on a bulk-list.
+	struct list_head bulk_head[FREE_N_CHANNELS];
+	atomic_t bulk_count[FREE_N_CHANNELS];
+
+	struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
+	raw_spinlock_t lock;
+	struct delayed_work monitor_work;
+	bool initialized;
+
+	struct delayed_work page_cache_work;
+	atomic_t backoff_page_cache_fill;
+	atomic_t work_in_progress;
+	struct hrtimer hrtimer;
+
+	struct llist_head bkvcache;
+	int nr_bkv_objs;
+};
-- 
2.39.5