ida: Move ida_bitmap to a percpu variable

When we preload the IDA, we allocate an IDA bitmap.  Instead of storing
that preallocated bitmap in the IDA, we store it in a percpu variable.
Generally there are more IDAs in the system than CPUs, so this cuts down
on the number of preallocated bitmaps that are unused, and about half
of the IDA users did not call ida_destroy() so they were leaking IDA
bitmaps.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

include/linux/idr.h

@@ -14,6 +14,7 @@
 
 #include <linux/radix-tree.h>
 #include <linux/gfp.h>
+#include <linux/percpu.h>
 
 struct idr {
 	struct radix_tree_root	idr_rt;
@@ -171,9 +172,10 @@ struct ida_bitmap {
 	unsigned long		bitmap[IDA_BITMAP_LONGS];
 };
 
+DECLARE_PER_CPU(struct ida_bitmap *, ida_bitmap);
+
 struct ida {
 	struct radix_tree_root	ida_rt;
-	struct ida_bitmap	*free_bitmap;
 };
 
 #define IDA_INIT	{						\
@@ -193,7 +195,6 @@ void ida_simple_remove(struct ida *ida, unsigned int id);
 static inline void ida_init(struct ida *ida)
 {
 	INIT_RADIX_TREE(&ida->ida_rt, IDR_RT_MARKER | GFP_NOWAIT);
-	ida->free_bitmap = NULL;
 }
 
 /**

lib/idr.c

@@ -4,6 +4,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 
+DEFINE_PER_CPU(struct ida_bitmap *, ida_bitmap);
 static DEFINE_SPINLOCK(simple_ida_lock);
 
 /**
@@ -193,38 +194,6 @@ EXPORT_SYMBOL(idr_replace);
  * limitation, it should be quite straightforward to raise the maximum.
  */
 
-/**
- * ida_pre_get - reserve resources for ida allocation
- * @ida: ida handle
- * @gfp: memory allocation flags
- *
- * This function should be called before calling ida_get_new_above().  If it
- * is unable to allocate memory, it will return %0.  On success, it returns %1.
- */
-int ida_pre_get(struct ida *ida, gfp_t gfp)
-{
-	struct ida_bitmap *bitmap;
-
-	/*
-	 * This looks weird, but the IDA API has no preload_end() equivalent.
-	 * Instead, ida_get_new() can return -EAGAIN, prompting the caller
-	 * to return to the ida_pre_get() step.
-	 */
-	idr_preload(gfp);
-	idr_preload_end();
-
-	if (!ida->free_bitmap) {
-		bitmap = kmalloc(sizeof(struct ida_bitmap), gfp);
-		if (!bitmap)
-			return 0;
-		bitmap = xchg(&ida->free_bitmap, bitmap);
-		kfree(bitmap);
-	}
-
-	return 1;
-}
-EXPORT_SYMBOL(ida_pre_get);
-
 #define IDA_MAX (0x80000000U / IDA_BITMAP_BITS)
 
 /**
@@ -292,10 +261,9 @@ int ida_get_new_above(struct ida *ida, int start, int *id)
 			new += bit;
 			if (new < 0)
 				return -ENOSPC;
-			bitmap = ida->free_bitmap;
+			bitmap = this_cpu_xchg(ida_bitmap, NULL);
 			if (!bitmap)
 				return -EAGAIN;
-			ida->free_bitmap = NULL;
 			memset(bitmap, 0, sizeof(*bitmap));
 			__set_bit(bit, bitmap->bitmap);
 			radix_tree_iter_replace(root, &iter, slot, bitmap);
@@ -361,9 +329,6 @@ void ida_destroy(struct ida *ida)
 		kfree(bitmap);
 		radix_tree_iter_delete(&ida->ida_rt, &iter, slot);
 	}
-
-	kfree(ida->free_bitmap);
-	ida->free_bitmap = NULL;
 }
 EXPORT_SYMBOL(ida_destroy);
 

lib/radix-tree.c

@@ -69,6 +69,14 @@ static struct kmem_cache *radix_tree_node_cachep;
 						RADIX_TREE_MAP_SHIFT))
 #define IDR_PRELOAD_SIZE	(IDR_MAX_PATH * 2 - 1)
 
+/*
+ * The IDA is even shorter since it uses a bitmap at the last level.
+ */
+#define IDA_INDEX_BITS		(8 * sizeof(int) - 1 - ilog2(IDA_BITMAP_BITS))
+#define IDA_MAX_PATH		(DIV_ROUND_UP(IDA_INDEX_BITS, \
+						RADIX_TREE_MAP_SHIFT))
+#define IDA_PRELOAD_SIZE	(IDA_MAX_PATH * 2 - 1)
+
 /*
  * Per-cpu pool of preloaded nodes
  */
@@ -346,9 +354,8 @@ static void dump_ida_node(void *entry, unsigned long index)
 static void ida_dump(struct ida *ida)
 {
 	struct radix_tree_root *root = &ida->ida_rt;
-	pr_debug("ida: %p %p free %d bitmap %p\n", ida, root->rnode,
-				root->gfp_mask >> ROOT_TAG_SHIFT,
-				ida->free_bitmap);
+	pr_debug("ida: %p node %p free %d\n", ida, root->rnode,
+				root->gfp_mask >> ROOT_TAG_SHIFT);
 	dump_ida_node(root->rnode, 0);
 }
 #endif
@@ -2080,6 +2087,36 @@ void idr_preload(gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(idr_preload);
 
+/**
+ * ida_pre_get - reserve resources for ida allocation
+ * @ida: ida handle
+ * @gfp: memory allocation flags
+ *
+ * This function should be called before calling ida_get_new_above().  If it
+ * is unable to allocate memory, it will return %0.  On success, it returns %1.
+ */
+int ida_pre_get(struct ida *ida, gfp_t gfp)
+{
+	__radix_tree_preload(gfp, IDA_PRELOAD_SIZE);
+	/*
+	 * The IDA API has no preload_end() equivalent.  Instead,
+	 * ida_get_new() can return -EAGAIN, prompting the caller
+	 * to return to the ida_pre_get() step.
+	 */
+	preempt_enable();
+
+	if (!this_cpu_read(ida_bitmap)) {
+		struct ida_bitmap *bitmap = kmalloc(sizeof(*bitmap), gfp);
+		if (!bitmap)
+			return 0;
+		bitmap = this_cpu_cmpxchg(ida_bitmap, NULL, bitmap);
+		kfree(bitmap);
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL(ida_pre_get);
+
 void **idr_get_free(struct radix_tree_root *root,
 			struct radix_tree_iter *iter, gfp_t gfp, int end)
 {
@@ -2219,6 +2256,8 @@ static int radix_tree_cpu_dead(unsigned int cpu)
 		kmem_cache_free(radix_tree_node_cachep, node);
 		rtp->nr--;
 	}
+	kfree(per_cpu(ida_bitmap, cpu));
+	per_cpu(ida_bitmap, cpu) = NULL;
 	return 0;
 }
 

tools/testing/radix-tree/linux/kernel.h

@@ -24,6 +24,4 @@
 
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 
-#define xchg(ptr, x)	uatomic_xchg(ptr, x)
-
 #endif /* _KERNEL_H */

tools/testing/radix-tree/linux/percpu.h

@@ -1,7 +1,10 @@
-
+#define DECLARE_PER_CPU(type, val) extern type val
 #define DEFINE_PER_CPU(type, val) type val
 
 #define __get_cpu_var(var)	var
 #define this_cpu_ptr(var)	var
+#define this_cpu_read(var)	var
+#define this_cpu_xchg(var, val)		uatomic_xchg(&var, val)
+#define this_cpu_cmpxchg(var, old, new)	uatomic_cmpxchg(&var, old, new)
 #define per_cpu_ptr(ptr, cpu)   ({ (void)(cpu); (ptr); })
 #define per_cpu(var, cpu)	(*per_cpu_ptr(&(var), cpu))