lttng lib: lttng priority heap

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/lttng/lib/prio_heap/lttng_prio_heap.c

+/*
+ * lttng_prio_heap.c
+ *
+ * Priority heap containing pointers. Based on CLRS, chapter 6.
+ *
+ * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ */
+
+#include <linux/slab.h>
+#include "lttng_prio_heap.h"
+
+#ifdef DEBUG_HEAP
+void lttng_check_heap(const struct lttng_ptr_heap *heap)
+{
+	size_t i;
+
+	if (!heap->len)
+		return;
+
+	for (i = 1; i < heap->len; i++)
+		WARN_ON_ONCE(!heap->gt(heap->ptrs[i], heap->ptrs[0]));
+}
+#endif
+
+static
+size_t parent(size_t i)
+{
+	return (i -1) >> 1;
+}
+
+static
+size_t left(size_t i)
+{
+	return (i << 1) + 1;
+}
+
+static
+size_t right(size_t i)
+{
+	return (i << 1) + 2;
+}
+
+/*
+ * Copy of heap->ptrs pointer is invalid after heap_grow.
+ */
+static
+int heap_grow(struct lttng_ptr_heap *heap, size_t new_len)
+{
+	void **new_ptrs;
+
+	if (heap->alloc_len >= new_len)
+		return 0;
+
+	heap->alloc_len = max_t(size_t, new_len, heap->alloc_len << 1);
+	new_ptrs = kmalloc(heap->alloc_len * sizeof(void *), heap->gfpmask);
+	if (!new_ptrs)
+		return -ENOMEM;
+	if (heap->ptrs)
+		memcpy(new_ptrs, heap->ptrs, heap->len * sizeof(void *));
+	kfree(heap->ptrs);
+	heap->ptrs = new_ptrs;
+	return 0;
+}
+
+static
+int heap_set_len(struct lttng_ptr_heap *heap, size_t new_len)
+{
+	int ret;
+
+	ret = heap_grow(heap, new_len);
+	if (ret)
+		return ret;
+	heap->len = new_len;
+	return 0;
+}
+
+int lttng_heap_init(struct lttng_ptr_heap *heap, size_t alloc_len,
+	      gfp_t gfpmask, int gt(void *a, void *b))
+{
+	heap->ptrs = NULL;
+	heap->len = 0;
+	heap->alloc_len = 0;
+	heap->gt = gt;
+	heap->gfpmask = gfpmask;
+	/*
+	 * Minimum size allocated is 1 entry to ensure memory allocation
+	 * never fails within heap_replace_max.
+	 */
+	return heap_grow(heap, max_t(size_t, 1, alloc_len));
+}
+
+void lttng_heap_free(struct lttng_ptr_heap *heap)
+{
+	kfree(heap->ptrs);
+}
+
+static void heapify(struct lttng_ptr_heap *heap, size_t i)
+{
+	void **ptrs = heap->ptrs;
+	size_t l, r, largest;
+
+	for (;;) {
+		void *tmp;
+
+		l = left(i);
+		r = right(i);
+		if (l < heap->len && heap->gt(ptrs[l], ptrs[i]))
+			largest = l;
+		else
+			largest = i;
+		if (r < heap->len && heap->gt(ptrs[r], ptrs[largest]))
+			largest = r;
+		if (largest == i)
+			break;
+		tmp = ptrs[i];
+		ptrs[i] = ptrs[largest];
+		ptrs[largest] = tmp;
+		i = largest;
+	}
+	lttng_check_heap(heap);
+}
+
+void *lttng_heap_replace_max(struct lttng_ptr_heap *heap, void *p)
+{
+	void *res;
+
+	if (!heap->len) {
+		(void) heap_set_len(heap, 1);
+		heap->ptrs[0] = p;
+		lttng_check_heap(heap);
+		return NULL;
+	}
+
+	/* Replace the current max and heapify */
+	res = heap->ptrs[0];
+	heap->ptrs[0] = p;
+	heapify(heap, 0);
+	return res;
+}
+
+int lttng_heap_insert(struct lttng_ptr_heap *heap, void *p)
+{
+	void **ptrs;
+	size_t pos;
+	int ret;
+
+	ret = heap_set_len(heap, heap->len + 1);
+	if (ret)
+		return ret;
+	ptrs = heap->ptrs;
+	pos = heap->len - 1;
+	while (pos > 0 && heap->gt(p, ptrs[parent(pos)])) {
+		/* Move parent down until we find the right spot */
+		ptrs[pos] = ptrs[parent(pos)];
+		pos = parent(pos);
+	}
+	ptrs[pos] = p;
+	lttng_check_heap(heap);
+	return 0;
+}
+
+void *lttng_heap_remove(struct lttng_ptr_heap *heap)
+{
+	switch (heap->len) {
+	case 0:
+		return NULL;
+	case 1:
+		(void) heap_set_len(heap, 0);
+		return heap->ptrs[0];
+	}
+	/* Shrink, replace the current max by previous last entry and heapify */
+	heap_set_len(heap, heap->len - 1);
+	/* len changed. previous last entry is at heap->len */
+	return lttng_heap_replace_max(heap, heap->ptrs[heap->len]);
+}
+
+void *lttng_heap_cherrypick(struct lttng_ptr_heap *heap, void *p)
+{
+	size_t pos, len = heap->len;
+
+	for (pos = 0; pos < len; pos++)
+		if (heap->ptrs[pos] == p)
+			goto found;
+	return NULL;
+found:
+	if (heap->len == 1) {
+		(void) heap_set_len(heap, 0);
+		lttng_check_heap(heap);
+		return heap->ptrs[0];
+	}
+	/* Replace p with previous last entry and heapify. */
+	heap_set_len(heap, heap->len - 1);
+	/* len changed. previous last entry is at heap->len */
+	heap->ptrs[pos] = heap->ptrs[heap->len];
+	heapify(heap, pos);
+	return p;
+}

drivers/staging/lttng/lib/prio_heap/lttng_prio_heap.h

+#ifndef _LTTNG_PRIO_HEAP_H
+#define _LTTNG_PRIO_HEAP_H
+
+/*
+ * lttng_prio_heap.h
+ *
+ * Priority heap containing pointers. Based on CLRS, chapter 6.
+ *
+ * Copyright 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ */
+
+#include <linux/gfp.h>
+
+struct lttng_ptr_heap {
+	size_t len, alloc_len;
+	void **ptrs;
+	int (*gt)(void *a, void *b);
+	gfp_t gfpmask;
+};
+
+#ifdef DEBUG_HEAP
+void lttng_check_heap(const struct lttng_ptr_heap *heap);
+#else
+static inline
+void lttng_check_heap(const struct lttng_ptr_heap *heap)
+{
+}
+#endif
+
+/**
+ * lttng_heap_maximum - return the largest element in the heap
+ * @heap: the heap to be operated on
+ *
+ * Returns the largest element in the heap, without performing any modification
+ * to the heap structure. Returns NULL if the heap is empty.
+ */
+static inline void *lttng_heap_maximum(const struct lttng_ptr_heap *heap)
+{
+	lttng_check_heap(heap);
+	return heap->len ? heap->ptrs[0] : NULL;
+}
+
+/**
+ * lttng_heap_init - initialize the heap
+ * @heap: the heap to initialize
+ * @alloc_len: number of elements initially allocated
+ * @gfp: allocation flags
+ * @gt: function to compare the elements
+ *
+ * Returns -ENOMEM if out of memory.
+ */
+extern int lttng_heap_init(struct lttng_ptr_heap *heap,
+		     size_t alloc_len, gfp_t gfpmask,
+		     int gt(void *a, void *b));
+
+/**
+ * lttng_heap_free - free the heap
+ * @heap: the heap to free
+ */
+extern void lttng_heap_free(struct lttng_ptr_heap *heap);
+
+/**
+ * lttng_heap_insert - insert an element into the heap
+ * @heap: the heap to be operated on
+ * @p: the element to add
+ *
+ * Insert an element into the heap.
+ *
+ * Returns -ENOMEM if out of memory.
+ */
+extern int lttng_heap_insert(struct lttng_ptr_heap *heap, void *p);
+
+/**
+ * lttng_heap_remove - remove the largest element from the heap
+ * @heap: the heap to be operated on
+ *
+ * Returns the largest element in the heap. It removes this element from the
+ * heap. Returns NULL if the heap is empty.
+ */
+extern void *lttng_heap_remove(struct lttng_ptr_heap *heap);
+
+/**
+ * lttng_heap_cherrypick - remove a given element from the heap
+ * @heap: the heap to be operated on
+ * @p: the element
+ *
+ * Remove the given element from the heap. Return the element if present, else
+ * return NULL. This algorithm has a complexity of O(n), which is higher than
+ * O(log(n)) provided by the rest of this API.
+ */
+extern void *lttng_heap_cherrypick(struct lttng_ptr_heap *heap, void *p);
+
+/**
+ * lttng_heap_replace_max - replace the the largest element from the heap
+ * @heap: the heap to be operated on
+ * @p: the pointer to be inserted as topmost element replacement
+ *
+ * Returns the largest element in the heap. It removes this element from the
+ * heap. The heap is rebalanced only once after the insertion. Returns NULL if
+ * the heap is empty.
+ *
+ * This is the equivalent of calling heap_remove() and then heap_insert(), but
+ * it only rebalances the heap once. It never allocates memory.
+ */
+extern void *lttng_heap_replace_max(struct lttng_ptr_heap *heap, void *p);
+
+#endif /* _LTTNG_PRIO_HEAP_H */