cfq-iosched: compact io_context radix_tree

Use small consequent indexes as radix tree keys instead of sparse cfqd address.

This change will reduce radix tree depth from 11 (6 for 32-bit hosts)
to 1 if host have <=64 disks under cfq control, or to 0 if there only one disk.
So, this patch save 10*560 bytes for each process (5*296 for 32-bit hosts)

For each cfqd allocate cic index from ida.
To unlink dead cic from tree without cfqd access store index into ->key.
(bit 0 -- dead mark, bits 1..30 -- index: ida produce id in range 0..2^31-1)

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 39 insertions, 5 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 407602350350..c72e5acc573d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -64,6 +64,9 @@ static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
 static struct completion *ioc_gone;
 static DEFINE_SPINLOCK(ioc_gone_lock);
 
+static DEFINE_SPINLOCK(cic_index_lock);
+static DEFINE_IDA(cic_index_ida);
+
 #define CFQ_PRIO_LISTS          IOPRIO_BE_NR
 #define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
 #define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)
@@ -271,6 +274,7 @@ struct cfq_data {
         unsigned int cfq_latency;
         unsigned int cfq_group_isolation;
 
+        unsigned int cic_index;
         struct list_head cic_list;
 
         /*
@@ -431,10 +435,11 @@ static inline void cic_set_cfqq(struct cfq_io_context *cic,
 }
 
 #define CIC_DEAD_KEY    1ul
+#define CIC_DEAD_INDEX_SHIFT    1
 
 static inline void *cfqd_dead_key(struct cfq_data *cfqd)
 {
-        return (void *)((unsigned long) cfqd | CIC_DEAD_KEY);
+        return (void *)(cfqd->cic_index << CIC_DEAD_INDEX_SHIFT | CIC_DEAD_KEY);
 }
 
 static inline struct cfq_data *cic_to_cfqd(struct cfq_io_context *cic)
@@ -2532,7 +2537,7 @@ static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
         BUG_ON(!(dead_key & CIC_DEAD_KEY));
 
         spin_lock_irqsave(&ioc->lock, flags);
-        radix_tree_delete(&ioc->radix_root, dead_key & ~CIC_DEAD_KEY);
+        radix_tree_delete(&ioc->radix_root, dead_key >> CIC_DEAD_INDEX_SHIFT);
         hlist_del_rcu(&cic->cic_list);
         spin_unlock_irqrestore(&ioc->lock, flags);
 
@@ -2906,7 +2911,7 @@ cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
 
         BUG_ON(ioc->ioc_data == cic);
 
-        radix_tree_delete(&ioc->radix_root, (unsigned long) cfqd);
+        radix_tree_delete(&ioc->radix_root, cfqd->cic_index);
         hlist_del_rcu(&cic->cic_list);
         spin_unlock_irqrestore(&ioc->lock, flags);
 
@@ -2934,7 +2939,7 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
         }
 
         do {
-                cic = radix_tree_lookup(&ioc->radix_root, (unsigned long) cfqd);
+                cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
                 rcu_read_unlock();
                 if (!cic)
                         break;
@@ -2971,7 +2976,7 @@ static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
 
                 spin_lock_irqsave(&ioc->lock, flags);
                 ret = radix_tree_insert(&ioc->radix_root,
-                                                (unsigned long) cfqd, cic);
+                                                cfqd->cic_index, cic);
                 if (!ret)
                         hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
                 spin_unlock_irqrestore(&ioc->lock, flags);
@@ -3723,10 +3728,32 @@ static void cfq_exit_queue(struct elevator_queue *e)
 
         cfq_shutdown_timer_wq(cfqd);
 
+        spin_lock(&cic_index_lock);
+        ida_remove(&cic_index_ida, cfqd->cic_index);
+        spin_unlock(&cic_index_lock);
+
         /* Wait for cfqg->blkg->key accessors to exit their grace periods. */
         call_rcu(&cfqd->rcu, cfq_cfqd_free);
 }
 
+static int cfq_alloc_cic_index(void)
+{
+        int index, error;
+
+        do {
+                if (!ida_pre_get(&cic_index_ida, GFP_KERNEL))
+                        return -ENOMEM;
+
+                spin_lock(&cic_index_lock);
+                error = ida_get_new(&cic_index_ida, &index);
+                spin_unlock(&cic_index_lock);
+                if (error && error != -EAGAIN)
+                        return error;
+        } while (error);
+
+        return index;
+}
+
 static void *cfq_init_queue(struct request_queue *q)
 {
         struct cfq_data *cfqd;
@@ -3734,10 +3761,16 @@ static void *cfq_init_queue(struct request_queue *q)
         struct cfq_group *cfqg;
         struct cfq_rb_root *st;
 
+        i = cfq_alloc_cic_index();
+        if (i < 0)
+                return NULL;
+
         cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
         if (!cfqd)
                 return NULL;
 
+        cfqd->cic_index = i;
+
         /* Init root service tree */
         cfqd->grp_service_tree = CFQ_RB_ROOT;
 
@@ -3999,6 +4032,7 @@ static void __exit cfq_exit(void)
          */
         if (elv_ioc_count_read(cfq_ioc_count))
                 wait_for_completion(&all_gone);
+        ida_destroy(&cic_index_ida);
         cfq_slab_kill();
 }