[PATCH v3 02/10] lib: introduce generic min max heap

[Ian Rogers <irogers@google.com>]

Based-on-work-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 include/linux/min_max_heap.h | 134 ++++++++++++++++++++++++
 lib/Kconfig.debug            |  10 ++
 lib/Makefile                 |   1 +
 lib/test_min_max_heap.c      | 194 +++++++++++++++++++++++++++++++++++
 4 files changed, 339 insertions(+)
 create mode 100644 include/linux/min_max_heap.h
 create mode 100644 lib/test_min_max_heap.c

diff --git a/include/linux/min_max_heap.h b/include/linux/min_max_heap.h
new file mode 100644
index 000000000000..ea7764a8252a
--- /dev/null
+++ b/include/linux/min_max_heap.h
@@ -0,0 +1,134 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MIN_MAX_HEAP_H
+#define _LINUX_MIN_MAX_HEAP_H
+
+#include <linux/bug.h>
+#include <linux/string.h>
+
+/*
+ * Data structure used to hold a min or max heap, the number of elements varies
+ * but the maximum size is fixed.
+ */
+struct min_max_heap {
+	/* Start of array holding the heap elements. */
+	void *data;
+	/* Number of elements currently in min-heap. */
+	int size;
+	/* Maximum number of elements that can be held in current storage. */
+	int cap;
+};
+
+struct min_max_heap_callbacks {
+	/* Size of elements in the heap. */
+	int elem_size;
+	/*
+	 * A function which returns *lhs < *rhs or *lhs > *rhs depending on
+	 * whether this is a min or a max heap. Note, another compare function
+	 * style in the kernel will return -ve, 0 and +ve and won't handle
+	 * minimum integer correctly if implemented as a subtract.
+	 */
+	bool (*cmp)(const void *lhs, const void *rhs);
+	/* Swap the element values at lhs with those at rhs. */
+	void (*swp)(void *lhs, void *rhs);
+};
+
+/* Sift the element at pos down the heap. */
+static inline void heapify(struct min_max_heap *heap, int pos,
+			const struct min_max_heap_callbacks *func) {
+	void *left_child, *right_child, *parent, *large_or_smallest;
+	char *data = (char *)heap->data;
+
+	for (;;) {
+		if (pos * 2 + 1 >= heap->size)
+			break;
+
+		left_child = data + ((pos * 2 + 1) * func->elem_size);
+		parent = data + (pos * func->elem_size);
+		large_or_smallest = parent;
+		if (func->cmp(left_child, large_or_smallest))
+			large_or_smallest = left_child;
+
+		if (pos * 2 + 2 < heap->size) {
+			right_child = data + ((pos * 2 + 2) * func->elem_size);
+			if (func->cmp(right_child, large_or_smallest))
+				large_or_smallest = right_child;
+		}
+		if (large_or_smallest == parent)
+			break;
+		func->swp(large_or_smallest, parent);
+		if (large_or_smallest == left_child)
+			pos = (pos * 2) + 1;
+		else
+			pos = (pos * 2) + 2;
+	}
+}
+
+/* Floyd's approach to heapification that is O(size). */
+static inline void
+heapify_all(struct min_max_heap *heap,
+	const struct min_max_heap_callbacks *func)
+{
+	int i;
+
+	for (i = heap->size / 2; i >= 0; i--)
+		heapify(heap, i, func);
+}
+
+/* Remove minimum element from the heap, O(log2(size)). */
+static inline void
+heap_pop(struct min_max_heap *heap, const struct min_max_heap_callbacks *func)
+{
+	char *data = (char *)heap->data;
+
+	if (WARN_ONCE(heap->size <= 0, "Popping an empty heap"))
+		return;
+
+	/* Place last element at the root (position 0) and then sift down. */
+	heap->size--;
+	memcpy(data, data + (heap->size * func->elem_size), func->elem_size);
+	heapify(heap, 0, func);
+}
+
+/*
+ * Remove the minimum element and then push the given element. The
+ * implementation performs 1 sift (O(log2(size))) and is therefore more
+ * efficient than a pop followed by a push that does 2.
+ */
+static void heap_pop_push(struct min_max_heap *heap,
+			const void *element,
+			const struct min_max_heap_callbacks *func)
+{
+	char *data = (char *)heap->data;
+
+	memcpy(data, element, func->elem_size);
+	heapify(heap, 0, func);
+}
+
+/* Push an element on to the heap, O(log2(size)). */
+static inline void
+heap_push(struct min_max_heap *heap, const void *element,
+	const struct min_max_heap_callbacks *func)
+{
+	void *child, *parent;
+	int pos;
+	char *data = (char *)heap->data;
+
+	if (WARN_ONCE(heap->size >= heap->cap, "Pushing on a full heap"))
+		return;
+
+	/* Place at the end of data. */
+	pos = heap->size;
+	memcpy(data + (pos * func->elem_size), element, func->elem_size);
+	heap->size++;
+
+	/* Sift up. */
+	for (; pos > 0; pos = (pos - 1) / 2) {
+		child = data + (pos * func->elem_size);
+		parent = data + ((pos - 1) / 2) * func->elem_size;
+		if (func->cmp(parent, child))
+			break;
+		func->swp(parent, child);
+	}
+}
+
+#endif /* _LINUX_MIN_MAX_HEAP_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93d97f9b0157..6a2cf82515eb 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1693,6 +1693,16 @@ config TEST_LIST_SORT
 
 	  If unsure, say N.
 
+config TEST_MIN_MAX_HEAP
+	tristate "Min-max heap test"
+	depends on DEBUG_KERNEL || m
+	help
+	  Enable this to turn on min-max heap function tests. This test is
+	  executed only once during system boot (so affects only boot time),
+	  or at module load time.
+
+	  If unsure, say N.
+
 config TEST_SORT
 	tristate "Array-based sort test"
 	depends on DEBUG_KERNEL || m
diff --git a/lib/Makefile b/lib/Makefile
index c5892807e06f..e73df06adaab 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -67,6 +67,7 @@ CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
 UBSAN_SANITIZE_test_ubsan.o := y
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
+obj-$(CONFIG_TEST_MIN_MAX_HEAP) += test_min_max_heap.o
 obj-$(CONFIG_TEST_LKM) += test_module.o
 obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
 obj-$(CONFIG_TEST_OVERFLOW) += test_overflow.o
diff --git a/lib/test_min_max_heap.c b/lib/test_min_max_heap.c
new file mode 100644
index 000000000000..72c756d96e5e
--- /dev/null
+++ b/lib/test_min_max_heap.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define pr_fmt(fmt) "min_max_heap_test: " fmt
+
+/*
+ * Test cases for the min max heap.
+ */
+
+#include <linux/log2.h>
+#include <linux/min_max_heap.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+
+static __init bool less_than(const void *lhs, const void *rhs)
+{
+	return *(int *)lhs < *(int *)rhs;
+}
+
+static __init bool greater_than(const void *lhs, const void *rhs)
+{
+	return *(int *)lhs > *(int *)rhs;
+}
+
+static __init void swap_ints(void *lhs, void *rhs)
+{
+	int temp = *(int *)lhs;
+
+	*(int *)lhs = *(int *)rhs;
+	*(int *)rhs = temp;
+}
+
+static __init int pop_verify_heap(bool min_heap,
+				struct min_max_heap *heap,
+				const struct min_max_heap_callbacks *funcs)
+{
+	int last;
+	int *values = (int *)heap->data;
+	int err = 0;
+
+	last = values[0];
+	heap_pop(heap, funcs);
+	while (heap->size > 0) {
+		if (min_heap) {
+			if (last > values[0]) {
+				pr_err("error: expected %d <= %d\n", last,
+					values[0]);
+				err++;
+			}
+		} else {
+			if (last < values[0]) {
+				pr_err("error: expected %d >= %d\n", last,
+					values[0]);
+				err++;
+			}
+		}
+		last = values[0];
+		heap_pop(heap, funcs);
+	}
+	return err;
+}
+
+static __init int test_heapify_all(bool min_heap)
+{
+	int values[] = { 3, 1, 2, 4, 0x8000000, 0x7FFFFFF, 0,
+			 -3, -1, -2, -4, 0x8000000, 0x7FFFFFF };
+	struct min_max_heap heap = {
+		.data = values,
+		.size = ARRAY_SIZE(values),
+		.cap =  ARRAY_SIZE(values),
+	};
+	struct min_max_heap_callbacks funcs = {
+		.elem_size = sizeof(int),
+		.cmp = min_heap ? less_than : greater_than,
+		.swp = swap_ints,
+	};
+	int i, err;
+
+	/* Test with known set of values. */
+	heapify_all(&heap, &funcs);
+	err = pop_verify_heap(min_heap, &heap, &funcs);
+
+
+	/* Test with randomly generated values. */
+	heap.size = ARRAY_SIZE(values);
+	for (i = 0; i < heap.size; i++)
+		values[i] = get_random_int();
+
+	heapify_all(&heap, &funcs);
+	err += pop_verify_heap(min_heap, &heap, &funcs);
+
+	return err;
+}
+
+static __init int test_heap_push(bool min_heap)
+{
+	const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
+			     -3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
+	int values[ARRAY_SIZE(data)];
+	struct min_max_heap heap = {
+		.data = values,
+		.size = 0,
+		.cap =  ARRAY_SIZE(values),
+	};
+	struct min_max_heap_callbacks funcs = {
+		.elem_size = sizeof(int),
+		.cmp = min_heap ? less_than : greater_than,
+		.swp = swap_ints,
+	};
+	int i, temp, err;
+
+	/* Test with known set of values copied from data. */
+	for (i = 0; i < ARRAY_SIZE(data); i++)
+		heap_push(&heap, &data[i], &funcs);
+
+	err = pop_verify_heap(min_heap, &heap, &funcs);
+
+	/* Test with randomly generated values. */
+	while (heap.size < heap.cap) {
+		temp = get_random_int();
+		heap_push(&heap, &temp, &funcs);
+	}
+	err += pop_verify_heap(min_heap, &heap, &funcs);
+
+	return err;
+}
+
+static __init int test_heap_pop_push(bool min_heap)
+{
+	const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
+			     -3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
+	int values[ARRAY_SIZE(data)];
+	struct min_max_heap heap = {
+		.data = values,
+		.size = 0,
+		.cap =  ARRAY_SIZE(values),
+	};
+	struct min_max_heap_callbacks funcs = {
+		.elem_size = sizeof(int),
+		.cmp = min_heap ? less_than : greater_than,
+		.swp = swap_ints,
+	};
+	int i, temp, err;
+
+	/* Fill values with data to pop and replace. */
+	temp = min_heap ? 0x80000000 : 0x7FFFFFFF;
+	for (i = 0; i < ARRAY_SIZE(data); i++)
+		heap_push(&heap, &temp, &funcs);
+
+	/* Test with known set of values copied from data. */
+	for (i = 0; i < ARRAY_SIZE(data); i++)
+		heap_pop_push(&heap, &data[i], &funcs);
+
+	err = pop_verify_heap(min_heap, &heap, &funcs);
+
+	heap.size = 0;
+	for (i = 0; i < ARRAY_SIZE(data); i++)
+		heap_push(&heap, &temp, &funcs);
+
+	/* Test with randomly generated values. */
+	for (i = 0; i < ARRAY_SIZE(data); i++) {
+		temp = get_random_int();
+		heap_pop_push(&heap, &temp, &funcs);
+	}
+	err += pop_verify_heap(min_heap, &heap, &funcs);
+
+	return err;
+}
+
+static int __init test_min_max_heap_init(void)
+{
+	int err = 0;
+
+	err += test_heapify_all(true);
+	err += test_heapify_all(false);
+	err += test_heap_push(true);
+	err += test_heap_push(false);
+	err += test_heap_pop_push(true);
+	err += test_heap_pop_push(false);
+	if (err) {
+		pr_err("test failed with %d errors\n", err);
+		return -EINVAL;
+	}
+	pr_info("test passed\n");
+	return 0;
+}
+module_init(test_min_max_heap_init);
+
+static void __exit test_min_max_heap_exit(void)
+{
+	/* do nothing */
+}
+module_exit(test_min_max_heap_exit);
+
+MODULE_LICENSE("GPL");
-- 
2.24.0.432.g9d3f5f5b63-goog