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