1 files changed, 399 insertions, 58 deletions

diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
index d52daf45861b..79ddc0adbf2b 100644
--- a/include/linux/min_heap.h
+++ b/include/linux/min_heap.h
@@ -6,131 +6,472 @@
 #include <linux/string.h>
 #include <linux/types.h>
 
+/*
+ * The Min Heap API provides utilities for managing min-heaps, a binary tree
+ * structure where each node's value is less than or equal to its children's
+ * values, ensuring the smallest element is at the root.
+ *
+ * Users should avoid directly calling functions prefixed with __min_heap_*().
+ * Instead, use the provided macro wrappers.
+ *
+ * For further details and examples, refer to Documentation/core-api/min_heap.rst.
+ */
+
 /**
- * struct min_heap - Data structure to hold a min-heap.
- * @data: Start of array holding the heap elements.
+ * Data structure to hold a min-heap.
  * @nr: Number of elements currently in the heap.
  * @size: Maximum number of elements that can be held in current storage.
+ * @data: Pointer to the start of array holding the heap elements.
+ * @preallocated: Start of the static preallocated array holding the heap elements.
  */
-struct min_heap {
-	void *data;
-	int nr;
-	int size;
-};
+#define MIN_HEAP_PREALLOCATED(_type, _name, _nr)	\
+struct _name {	\
+	size_t nr;	\
+	size_t size;	\
+	_type *data;	\
+	_type preallocated[_nr];	\
+}
+
+#define DEFINE_MIN_HEAP(_type, _name) MIN_HEAP_PREALLOCATED(_type, _name, 0)
+
+typedef DEFINE_MIN_HEAP(char, min_heap_char) min_heap_char;
+
+#define __minheap_cast(_heap)		(typeof((_heap)->data[0]) *)
+#define __minheap_obj_size(_heap)	sizeof((_heap)->data[0])
 
 /**
  * struct min_heap_callbacks - Data/functions to customise the min_heap.
- * @elem_size: The nr of each element in bytes.
  * @less: Partial order function for this heap.
  * @swp: Swap elements function.
  */
 struct min_heap_callbacks {
-	int elem_size;
-	bool (*less)(const void *lhs, const void *rhs);
-	void (*swp)(void *lhs, void *rhs);
+	bool (*less)(const void *lhs, const void *rhs, void *args);
+	void (*swp)(void *lhs, void *rhs, void *args);
 };
 
+/**
+ * is_aligned - is this pointer & size okay for word-wide copying?
+ * @base: pointer to data
+ * @size: size of each element
+ * @align: required alignment (typically 4 or 8)
+ *
+ * Returns true if elements can be copied using word loads and stores.
+ * The size must be a multiple of the alignment, and the base address must
+ * be if we do not have CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
+ *
+ * For some reason, gcc doesn't know to optimize "if (a & mask || b & mask)"
+ * to "if ((a | b) & mask)", so we do that by hand.
+ */
+__attribute_const__ __always_inline
+static bool is_aligned(const void *base, size_t size, unsigned char align)
+{
+	unsigned char lsbits = (unsigned char)size;
+
+	(void)base;
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+	lsbits |= (unsigned char)(uintptr_t)base;
+#endif
+	return (lsbits & (align - 1)) == 0;
+}
+
+/**
+ * swap_words_32 - swap two elements in 32-bit chunks
+ * @a: pointer to the first element to swap
+ * @b: pointer to the second element to swap
+ * @n: element size (must be a multiple of 4)
+ *
+ * Exchange the two objects in memory.  This exploits base+index addressing,
+ * which basically all CPUs have, to minimize loop overhead computations.
+ *
+ * For some reason, on x86 gcc 7.3.0 adds a redundant test of n at the
+ * bottom of the loop, even though the zero flag is still valid from the
+ * subtract (since the intervening mov instructions don't alter the flags).
+ * Gcc 8.1.0 doesn't have that problem.
+ */
+static __always_inline
+void swap_words_32(void *a, void *b, size_t n)
+{
+	do {
+		u32 t = *(u32 *)(a + (n -= 4));
+		*(u32 *)(a + n) = *(u32 *)(b + n);
+		*(u32 *)(b + n) = t;
+	} while (n);
+}
+
+/**
+ * swap_words_64 - swap two elements in 64-bit chunks
+ * @a: pointer to the first element to swap
+ * @b: pointer to the second element to swap
+ * @n: element size (must be a multiple of 8)
+ *
+ * Exchange the two objects in memory.  This exploits base+index
+ * addressing, which basically all CPUs have, to minimize loop overhead
+ * computations.
+ *
+ * We'd like to use 64-bit loads if possible.  If they're not, emulating
+ * one requires base+index+4 addressing which x86 has but most other
+ * processors do not.  If CONFIG_64BIT, we definitely have 64-bit loads,
+ * but it's possible to have 64-bit loads without 64-bit pointers (e.g.
+ * x32 ABI).  Are there any cases the kernel needs to worry about?
+ */
+static __always_inline
+void swap_words_64(void *a, void *b, size_t n)
+{
+	do {
+#ifdef CONFIG_64BIT
+		u64 t = *(u64 *)(a + (n -= 8));
+		*(u64 *)(a + n) = *(u64 *)(b + n);
+		*(u64 *)(b + n) = t;
+#else
+		/* Use two 32-bit transfers to avoid base+index+4 addressing */
+		u32 t = *(u32 *)(a + (n -= 4));
+		*(u32 *)(a + n) = *(u32 *)(b + n);
+		*(u32 *)(b + n) = t;
+
+		t = *(u32 *)(a + (n -= 4));
+		*(u32 *)(a + n) = *(u32 *)(b + n);
+		*(u32 *)(b + n) = t;
+#endif
+	} while (n);
+}
+
+/**
+ * swap_bytes - swap two elements a byte at a time
+ * @a: pointer to the first element to swap
+ * @b: pointer to the second element to swap
+ * @n: element size
+ *
+ * This is the fallback if alignment doesn't allow using larger chunks.
+ */
+static __always_inline
+void swap_bytes(void *a, void *b, size_t n)
+{
+	do {
+		char t = ((char *)a)[--n];
+		((char *)a)[n] = ((char *)b)[n];
+		((char *)b)[n] = t;
+	} while (n);
+}
+
+/*
+ * The values are arbitrary as long as they can't be confused with
+ * a pointer, but small integers make for the smallest compare
+ * instructions.
+ */
+#define SWAP_WORDS_64 ((void (*)(void *, void *, void *))0)
+#define SWAP_WORDS_32 ((void (*)(void *, void *, void *))1)
+#define SWAP_BYTES    ((void (*)(void *, void *, void *))2)
+
+/*
+ * Selects the appropriate swap function based on the element size.
+ */
+static __always_inline
+void *select_swap_func(const void *base, size_t size)
+{
+	if (is_aligned(base, size, 8))
+		return SWAP_WORDS_64;
+	else if (is_aligned(base, size, 4))
+		return SWAP_WORDS_32;
+	else
+		return SWAP_BYTES;
+}
+
+static __always_inline
+void do_swap(void *a, void *b, size_t size, void (*swap_func)(void *lhs, void *rhs, void *args),
+	     void *priv)
+{
+	if (swap_func == SWAP_WORDS_64)
+		swap_words_64(a, b, size);
+	else if (swap_func == SWAP_WORDS_32)
+		swap_words_32(a, b, size);
+	else if (swap_func == SWAP_BYTES)
+		swap_bytes(a, b, size);
+	else
+		swap_func(a, b, priv);
+}
+
+/**
+ * parent - given the offset of the child, find the offset of the parent.
+ * @i: the offset of the heap element whose parent is sought.  Non-zero.
+ * @lsbit: a precomputed 1-bit mask, equal to "size & -size"
+ * @size: size of each element
+ *
+ * In terms of array indexes, the parent of element j = @i/@size is simply
+ * (j-1)/2.  But when working in byte offsets, we can't use implicit
+ * truncation of integer divides.
+ *
+ * Fortunately, we only need one bit of the quotient, not the full divide.
+ * @size has a least significant bit.  That bit will be clear if @i is
+ * an even multiple of @size, and set if it's an odd multiple.
+ *
+ * Logically, we're doing "if (i & lsbit) i -= size;", but since the
+ * branch is unpredictable, it's done with a bit of clever branch-free
+ * code instead.
+ */
+__attribute_const__ __always_inline
+static size_t parent(size_t i, unsigned int lsbit, size_t size)
+{
+	i -= size;
+	i -= size & -(i & lsbit);
+	return i / 2;
+}
+
+/* Initialize a min-heap. */
+static __always_inline
+void __min_heap_init_inline(min_heap_char *heap, void *data, size_t size)
+{
+	heap->nr = 0;
+	heap->size = size;
+	if (data)
+		heap->data = data;
+	else
+		heap->data = heap->preallocated;
+}
+
+#define min_heap_init_inline(_heap, _data, _size)	\
+	__min_heap_init_inline(container_of(&(_heap)->nr, min_heap_char, nr), _data, _size)
+
+/* Get the minimum element from the heap. */
+static __always_inline
+void *__min_heap_peek_inline(struct min_heap_char *heap)
+{
+	return heap->nr ? heap->data : NULL;
+}
+
+#define min_heap_peek_inline(_heap)	\
+	(__minheap_cast(_heap)	\
+	 __min_heap_peek_inline(container_of(&(_heap)->nr, min_heap_char, nr)))
+
+/* Check if the heap is full. */
+static __always_inline
+bool __min_heap_full_inline(min_heap_char *heap)
+{
+	return heap->nr == heap->size;
+}
+
+#define min_heap_full_inline(_heap)	\
+	__min_heap_full_inline(container_of(&(_heap)->nr, min_heap_char, nr))
+
 /* Sift the element at pos down the heap. */
 static __always_inline
-void min_heapify(struct min_heap *heap, int pos,
-		const struct min_heap_callbacks *func)
+void __min_heap_sift_down_inline(min_heap_char *heap, size_t pos, size_t elem_size,
+				 const struct min_heap_callbacks *func, void *args)
 {
-	void *left, *right;
+	const unsigned long lsbit = elem_size & -elem_size;
 	void *data = heap->data;
-	void *root = data + pos * func->elem_size;
-	int i = pos, j;
+	void (*swp)(void *lhs, void *rhs, void *args) = func->swp;
+	/* pre-scale counters for performance */
+	size_t a = pos * elem_size;
+	size_t b, c, d;
+	size_t n = heap->nr * elem_size;
+
+	if (!swp)
+		swp = select_swap_func(data, elem_size);
 
 	/* Find the sift-down path all the way to the leaves. */
-	for (;;) {
-		if (i * 2 + 2 >= heap->nr)
-			break;
-		left = data + (i * 2 + 1) * func->elem_size;
-		right = data + (i * 2 + 2) * func->elem_size;
-		i = func->less(left, right) ? i * 2 + 1 : i * 2 + 2;
-	}
+	for (b = a; c = 2 * b + elem_size, (d = c + elem_size) < n;)
+		b = func->less(data + c, data + d, args) ? c : d;
 
 	/* Special case for the last leaf with no sibling. */
-	if (i * 2 + 2 == heap->nr)
-		i = i * 2 + 1;
+	if (d == n)
+		b = c;
 
 	/* Backtrack to the correct location. */
-	while (i != pos && func->less(root, data + i * func->elem_size))
-		i = (i - 1) / 2;
+	while (b != a && func->less(data + a, data + b, args))
+		b = parent(b, lsbit, elem_size);
 
 	/* Shift the element into its correct place. */
-	j = i;
-	while (i != pos) {
-		i = (i - 1) / 2;
-		func->swp(data + i * func->elem_size, data + j * func->elem_size);
+	c = b;
+	while (b != a) {
+		b = parent(b, lsbit, elem_size);
+		do_swap(data + b, data + c, elem_size, swp, args);
 	}
 }
 
+#define min_heap_sift_down_inline(_heap, _pos, _func, _args)	\
+	__min_heap_sift_down_inline(container_of(&(_heap)->nr, min_heap_char, nr), _pos,	\
+				    __minheap_obj_size(_heap), _func, _args)
+
+/* Sift up ith element from the heap, O(log2(nr)). */
+static __always_inline
+void __min_heap_sift_up_inline(min_heap_char *heap, size_t elem_size, size_t idx,
+			       const struct min_heap_callbacks *func, void *args)
+{
+	const unsigned long lsbit = elem_size & -elem_size;
+	void *data = heap->data;
+	void (*swp)(void *lhs, void *rhs, void *args) = func->swp;
+	/* pre-scale counters for performance */
+	size_t a = idx * elem_size, b;
+
+	if (!swp)
+		swp = select_swap_func(data, elem_size);
+
+	while (a) {
+		b = parent(a, lsbit, elem_size);
+		if (func->less(data + b, data + a, args))
+			break;
+		do_swap(data + a, data + b, elem_size, swp, args);
+		a = b;
+	}
+}
+
+#define min_heap_sift_up_inline(_heap, _idx, _func, _args)	\
+	__min_heap_sift_up_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+				  __minheap_obj_size(_heap), _idx, _func, _args)
+
 /* Floyd's approach to heapification that is O(nr). */
 static __always_inline
-void min_heapify_all(struct min_heap *heap,
-		const struct min_heap_callbacks *func)
+void __min_heapify_all_inline(min_heap_char *heap, size_t elem_size,
+			      const struct min_heap_callbacks *func, void *args)
 {
-	int i;
+	ssize_t i;
 
 	for (i = heap->nr / 2 - 1; i >= 0; i--)
-		min_heapify(heap, i, func);
+		__min_heap_sift_down_inline(heap, i, elem_size, func, args);
 }
 
+#define min_heapify_all_inline(_heap, _func, _args)	\
+	__min_heapify_all_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+				 __minheap_obj_size(_heap), _func, _args)
+
 /* Remove minimum element from the heap, O(log2(nr)). */
 static __always_inline
-void min_heap_pop(struct min_heap *heap,
-		const struct min_heap_callbacks *func)
+bool __min_heap_pop_inline(min_heap_char *heap, size_t elem_size,
+			   const struct min_heap_callbacks *func, void *args)
 {
 	void *data = heap->data;
 
 	if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
-		return;
+		return false;
 
 	/* Place last element at the root (position 0) and then sift down. */
 	heap->nr--;
-	memcpy(data, data + (heap->nr * func->elem_size), func->elem_size);
-	min_heapify(heap, 0, func);
+	memcpy(data, data + (heap->nr * elem_size), elem_size);
+	__min_heap_sift_down_inline(heap, 0, elem_size, func, args);
+
+	return true;
 }
 
+#define min_heap_pop_inline(_heap, _func, _args)	\
+	__min_heap_pop_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			      __minheap_obj_size(_heap), _func, _args)
+
 /*
  * Remove the minimum element and then push the given element. The
  * implementation performs 1 sift (O(log2(nr))) and is therefore more
  * efficient than a pop followed by a push that does 2.
  */
 static __always_inline
-void min_heap_pop_push(struct min_heap *heap,
-		const void *element,
-		const struct min_heap_callbacks *func)
+void __min_heap_pop_push_inline(min_heap_char *heap, const void *element, size_t elem_size,
+				const struct min_heap_callbacks *func, void *args)
 {
-	memcpy(heap->data, element, func->elem_size);
-	min_heapify(heap, 0, func);
+	memcpy(heap->data, element, elem_size);
+	__min_heap_sift_down_inline(heap, 0, elem_size, func, args);
 }
 
+#define min_heap_pop_push_inline(_heap, _element, _func, _args)	\
+	__min_heap_pop_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+				   __minheap_obj_size(_heap), _func, _args)
+
 /* Push an element on to the heap, O(log2(nr)). */
 static __always_inline
-void min_heap_push(struct min_heap *heap, const void *element,
-		const struct min_heap_callbacks *func)
+bool __min_heap_push_inline(min_heap_char *heap, const void *element, size_t elem_size,
+			    const struct min_heap_callbacks *func, void *args)
 {
 	void *data = heap->data;
-	void *child, *parent;
-	int pos;
+	size_t pos;
 
 	if (WARN_ONCE(heap->nr >= heap->size, "Pushing on a full heap"))
-		return;
+		return false;
 
 	/* Place at the end of data. */
 	pos = heap->nr;
-	memcpy(data + (pos * func->elem_size), element, func->elem_size);
+	memcpy(data + (pos * elem_size), element, elem_size);
 	heap->nr++;
 
 	/* Sift child at pos up. */
-	for (; pos > 0; pos = (pos - 1) / 2) {
-		child = data + (pos * func->elem_size);
-		parent = data + ((pos - 1) / 2) * func->elem_size;
-		if (func->less(parent, child))
-			break;
-		func->swp(parent, child);
-	}
+	__min_heap_sift_up_inline(heap, elem_size, pos, func, args);
+
+	return true;
 }
 
+#define min_heap_push_inline(_heap, _element, _func, _args)	\
+	__min_heap_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+					    __minheap_obj_size(_heap), _func, _args)
+
+/* Remove ith element from the heap, O(log2(nr)). */
+static __always_inline
+bool __min_heap_del_inline(min_heap_char *heap, size_t elem_size, size_t idx,
+			   const struct min_heap_callbacks *func, void *args)
+{
+	void *data = heap->data;
+	void (*swp)(void *lhs, void *rhs, void *args) = func->swp;
+
+	if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
+		return false;
+
+	if (!swp)
+		swp = select_swap_func(data, elem_size);
+
+	/* Place last element at the root (position 0) and then sift down. */
+	heap->nr--;
+	if (idx == heap->nr)
+		return true;
+	do_swap(data + (idx * elem_size), data + (heap->nr * elem_size), elem_size, swp, args);
+	__min_heap_sift_up_inline(heap, elem_size, idx, func, args);
+	__min_heap_sift_down_inline(heap, idx, elem_size, func, args);
+
+	return true;
+}
+
+#define min_heap_del_inline(_heap, _idx, _func, _args)	\
+	__min_heap_del_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			      __minheap_obj_size(_heap), _idx, _func, _args)
+
+void __min_heap_init(min_heap_char *heap, void *data, size_t size);
+void *__min_heap_peek(struct min_heap_char *heap);
+bool __min_heap_full(min_heap_char *heap);
+void __min_heap_sift_down(min_heap_char *heap, size_t pos, size_t elem_size,
+			  const struct min_heap_callbacks *func, void *args);
+void __min_heap_sift_up(min_heap_char *heap, size_t elem_size, size_t idx,
+			const struct min_heap_callbacks *func, void *args);
+void __min_heapify_all(min_heap_char *heap, size_t elem_size,
+		       const struct min_heap_callbacks *func, void *args);
+bool __min_heap_pop(min_heap_char *heap, size_t elem_size,
+		    const struct min_heap_callbacks *func, void *args);
+void __min_heap_pop_push(min_heap_char *heap, const void *element, size_t elem_size,
+			 const struct min_heap_callbacks *func, void *args);
+bool __min_heap_push(min_heap_char *heap, const void *element, size_t elem_size,
+		     const struct min_heap_callbacks *func, void *args);
+bool __min_heap_del(min_heap_char *heap, size_t elem_size, size_t idx,
+		    const struct min_heap_callbacks *func, void *args);
+
+#define min_heap_init(_heap, _data, _size)	\
+	__min_heap_init(container_of(&(_heap)->nr, min_heap_char, nr), _data, _size)
+#define min_heap_peek(_heap)	\
+	(__minheap_cast(_heap) __min_heap_peek(container_of(&(_heap)->nr, min_heap_char, nr)))
+#define min_heap_full(_heap)	\
+	__min_heap_full(container_of(&(_heap)->nr, min_heap_char, nr))
+#define min_heap_sift_down(_heap, _pos, _func, _args)	\
+	__min_heap_sift_down(container_of(&(_heap)->nr, min_heap_char, nr), _pos,	\
+			     __minheap_obj_size(_heap), _func, _args)
+#define min_heap_sift_up(_heap, _idx, _func, _args)	\
+	__min_heap_sift_up(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			   __minheap_obj_size(_heap), _idx, _func, _args)
+#define min_heapify_all(_heap, _func, _args)	\
+	__min_heapify_all(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			  __minheap_obj_size(_heap), _func, _args)
+#define min_heap_pop(_heap, _func, _args)	\
+	__min_heap_pop(container_of(&(_heap)->nr, min_heap_char, nr),	\
+		       __minheap_obj_size(_heap), _func, _args)
+#define min_heap_pop_push(_heap, _element, _func, _args)	\
+	__min_heap_pop_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+			    __minheap_obj_size(_heap), _func, _args)
+#define min_heap_push(_heap, _element, _func, _args)	\
+	__min_heap_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+			__minheap_obj_size(_heap), _func, _args)
+#define min_heap_del(_heap, _idx, _func, _args)	\
+	__min_heap_del(container_of(&(_heap)->nr, min_heap_char, nr),	\
+		       __minheap_obj_size(_heap), _idx, _func, _args)
+
 #endif /* _LINUX_MIN_HEAP_H */