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From: Kuan-Wei Chiu <visitorckw@gmail.com>
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	Kuan-Wei Chiu <visitorckw@gmail.com>
Subject: [PATCH 04/13] lib min_heap: Add type safe interface
Date: Wed, 20 Mar 2024 01:59:56 +0800
Message-Id: <20240319180005.246930-5-visitorckw@gmail.com>
In-Reply-To: <20240319180005.246930-1-visitorckw@gmail.com>
References: <20240319180005.246930-1-visitorckw@gmail.com>
Precedence: bulk
MIME-Version: 1.0
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Introduce a type-safe interface for min_heap by adding small macro
wrappers around functions and using a 0-size array to store type
information. This enables the use of __minheap_cast and
__minheap_obj_size macros for type casting and obtaining element size.
The implementation draws inspiration from generic-radix-tree.h,
eliminating the need to pass element size in min_heap_callbacks.

Link: https://lkml.kernel.org/ioyfizrzq7w7mjrqcadtzsfgpuntowtjdw5pgn4qhvsdp4mqqg@nrlek5vmisbu
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 drivers/md/dm-vdo/repair.c     | 21 +++++-----
 drivers/md/dm-vdo/slab-depot.c | 13 +++---
 include/linux/min_heap.h       | 75 +++++++++++++++++++++++-----------
 kernel/events/core.c           | 35 ++++++++--------
 lib/test_min_heap.c            | 49 +++++++++++-----------
 5 files changed, 107 insertions(+), 86 deletions(-)

diff --git a/drivers/md/dm-vdo/repair.c b/drivers/md/dm-vdo/repair.c
index defc9359f10e..7663fa2098f4 100644
--- a/drivers/md/dm-vdo/repair.c
+++ b/drivers/md/dm-vdo/repair.c
@@ -51,6 +51,8 @@ struct recovery_point {
 	bool increment_applied;
 };
 
+MIN_HEAP(struct numbered_block_mapping *, replay_heap);
+
 struct repair_completion {
 	/* The completion header */
 	struct vdo_completion completion;
@@ -97,7 +99,7 @@ struct repair_completion {
 	 * order, then original journal order. This permits efficient iteration over the journal
 	 * entries in order.
 	 */
-	struct min_heap replay_heap;
+	struct replay_heap replay_heap;
 	/* Fields tracking progress through the journal entries. */
 	struct numbered_block_mapping *current_entry;
 	struct numbered_block_mapping *current_unfetched_entry;
@@ -163,25 +165,24 @@ static void swap_mappings(void *item1, void *item2)
 }
 
 static const struct min_heap_callbacks repair_min_heap = {
-	.elem_size = sizeof(struct numbered_block_mapping),
 	.less = mapping_is_less_than,
 	.swp = swap_mappings,
 };
 
 static struct numbered_block_mapping *sort_next_heap_element(struct repair_completion *repair)
 {
-	struct min_heap *heap = &repair->replay_heap;
+	struct replay_heap *heap = &repair->replay_heap;
 	struct numbered_block_mapping *last;
 
-	if (heap->nr == 0)
+	if (heap->heap.nr == 0)
 		return NULL;
 
 	/*
 	 * Swap the next heap element with the last one on the heap, popping it off the heap,
 	 * restore the heap invariant, and return a pointer to the popped element.
 	 */
-	last = &repair->entries[--heap->nr];
-	swap_mappings(heap->data, last);
+	last = &repair->entries[--heap->heap.nr];
+	swap_mappings(heap->heap.data, last);
 	min_heapify(heap, 0, &repair_min_heap);
 	return last;
 }
@@ -1117,11 +1118,9 @@ static void recover_block_map(struct vdo_completion *completion)
 	 * Organize the journal entries into a binary heap so we can iterate over them in sorted
 	 * order incrementally, avoiding an expensive sort call.
 	 */
-	repair->replay_heap = (struct min_heap) {
-		.data = repair->entries,
-		.nr = repair->block_map_entry_count,
-		.size = repair->block_map_entry_count,
-	};
+	repair->replay_heap.heap.data = repair->entries;
+	repair->replay_heap.heap.nr = repair->block_map_entry_count;
+	repair->replay_heap.heap.size = repair->block_map_entry_count;
 	min_heapify_all(&repair->replay_heap, &repair_min_heap);
 
 	vdo_log_info("Replaying %zu recovery entries into block map",
diff --git a/drivers/md/dm-vdo/slab-depot.c b/drivers/md/dm-vdo/slab-depot.c
index 46e4721e5b4f..3309480170c3 100644
--- a/drivers/md/dm-vdo/slab-depot.c
+++ b/drivers/md/dm-vdo/slab-depot.c
@@ -3309,7 +3309,6 @@ static void swap_slab_statuses(void *item1, void *item2)
 }
 
 static const struct min_heap_callbacks slab_status_min_heap = {
-	.elem_size = sizeof(struct slab_status),
 	.less = slab_status_is_less_than,
 	.swp = swap_slab_statuses,
 };
@@ -3509,7 +3508,7 @@ static int get_slab_statuses(struct block_allocator *allocator,
 static int __must_check vdo_prepare_slabs_for_allocation(struct block_allocator *allocator)
 {
 	struct slab_status current_slab_status;
-	struct min_heap heap;
+	MIN_HEAP(struct slab_status *, heap) heap;
 	int result;
 	struct slab_status *slab_statuses;
 	struct slab_depot *depot = allocator->depot;
@@ -3521,14 +3520,12 @@ static int __must_check vdo_prepare_slabs_for_allocation(struct block_allocator
 		return result;
 
 	/* Sort the slabs by cleanliness, then by emptiness hint. */
-	heap = (struct min_heap) {
-		.data = slab_statuses,
-		.nr = allocator->slab_count,
-		.size = allocator->slab_count,
-	};
+	heap.heap.data = slab_statuses;
+	heap.heap.nr = allocator->slab_count;
+	heap.heap.size = allocator->slab_count;
 	min_heapify_all(&heap, &slab_status_min_heap);
 
-	while (heap.nr > 0) {
+	while (heap.heap.nr > 0) {
 		bool high_priority;
 		struct vdo_slab *slab;
 		struct slab_journal *journal;
diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
index d52daf45861b..c3635a7fdb88 100644
--- a/include/linux/min_heap.h
+++ b/include/linux/min_heap.h
@@ -7,45 +7,59 @@
 #include <linux/types.h>
 
 /**
- * struct min_heap - Data structure to hold a min-heap.
+ * struct __min_heap - Data structure to hold a min-heap.
  * @data: Start of array holding the heap elements.
  * @nr: Number of elements currently in the heap.
  * @size: Maximum number of elements that can be held in current storage.
  */
-struct min_heap {
+struct __min_heap {
 	void *data;
 	int nr;
 	int size;
 };
 
+/*
+ * We use a 0 size array to stash the type we're storing without taking any
+ * space at runtime - then the various accessor macros can use typeof() to get
+ * to it for casts/sizeof - we also force the alignment so that storing a type
+ * with a ridiculous alignment doesn't blow up the alignment or size of the
+ * min_heap.
+ */
+#define MIN_HEAP(_type, _name)			\
+struct _name {				\
+	struct __min_heap	heap;		\
+	_type type[0] __aligned(1);	\
+}
+
+#define __minheap_cast(_heap)		(typeof((_heap)->type[0]) *)
+#define __minheap_obj_size(_heap)	sizeof((_heap)->type[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);
 };
 
 /* Sift the element at pos down the heap. */
 static __always_inline
-void min_heapify(struct min_heap *heap, int pos,
+void __min_heapify(struct __min_heap *heap, int pos, size_t elem_size,
 		const struct min_heap_callbacks *func)
 {
 	void *left, *right;
 	void *data = heap->data;
-	void *root = data + pos * func->elem_size;
+	void *root = data + pos * elem_size;
 	int i = pos, j;
 
 	/* 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;
+		left = data + (i * 2 + 1) * elem_size;
+		right = data + (i * 2 + 2) * elem_size;
 		i = func->less(left, right) ? i * 2 + 1 : i * 2 + 2;
 	}
 
@@ -54,31 +68,37 @@ void min_heapify(struct min_heap *heap, int pos,
 		i = i * 2 + 1;
 
 	/* Backtrack to the correct location. */
-	while (i != pos && func->less(root, data + i * func->elem_size))
+	while (i != pos && func->less(root, data + i * elem_size))
 		i = (i - 1) / 2;
 
 	/* 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);
+		func->swp(data + i * elem_size, data + j * elem_size);
 	}
 }
 
+#define min_heapify(_heap, _pos, _func)	\
+	__min_heapify(&(_heap)->heap, _pos, __minheap_obj_size(_heap), _func)
+
 /* Floyd's approach to heapification that is O(nr). */
 static __always_inline
-void min_heapify_all(struct min_heap *heap,
+void __min_heapify_all(struct __min_heap *heap, size_t elem_size,
 		const struct min_heap_callbacks *func)
 {
 	int i;
 
 	for (i = heap->nr / 2 - 1; i >= 0; i--)
-		min_heapify(heap, i, func);
+		__min_heapify(heap, i, elem_size, func);
 }
 
+#define min_heapify_all(_heap, _func)	\
+	__min_heapify_all(&(_heap)->heap, __minheap_obj_size(_heap), _func)
+
 /* Remove minimum element from the heap, O(log2(nr)). */
 static __always_inline
-void min_heap_pop(struct min_heap *heap,
+void __min_heap_pop(struct __min_heap *heap, size_t elem_size,
 		const struct min_heap_callbacks *func)
 {
 	void *data = heap->data;
@@ -88,27 +108,33 @@ void min_heap_pop(struct min_heap *heap,
 
 	/* 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_heapify(heap, 0, elem_size, func);
 }
 
+#define min_heap_pop(_heap, _func)	\
+	__min_heap_pop(&(_heap)->heap, __minheap_obj_size(_heap), _func)
+
 /*
  * 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,
+void __min_heap_pop_push(struct __min_heap *heap,
+		const void *element, size_t elem_size,
 		const struct min_heap_callbacks *func)
 {
-	memcpy(heap->data, element, func->elem_size);
-	min_heapify(heap, 0, func);
+	memcpy(heap->data, element, elem_size);
+	__min_heapify(heap, 0, elem_size, func);
 }
 
+#define min_heap_pop_push(_heap, _element, _func)	\
+	__min_heap_pop_push(&(_heap)->heap, _element, __minheap_obj_size(_heap), _func)
+
 /* Push an element on to the heap, O(log2(nr)). */
 static __always_inline
-void min_heap_push(struct min_heap *heap, const void *element,
+void __min_heap_push(struct __min_heap *heap, const void *element, size_t elem_size,
 		const struct min_heap_callbacks *func)
 {
 	void *data = heap->data;
@@ -120,17 +146,20 @@ void min_heap_push(struct min_heap *heap, const void *element,
 
 	/* 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;
+		child = data + (pos * elem_size);
+		parent = data + ((pos - 1) / 2) * elem_size;
 		if (func->less(parent, child))
 			break;
 		func->swp(parent, child);
 	}
 }
 
+#define min_heap_push(_heap, _element, _func)	\
+	__min_heap_push(&(_heap)->heap, _element, __minheap_obj_size(_heap), _func)
+
 #endif /* _LINUX_MIN_HEAP_H */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 10ac2db83f14..065dfaa8b009 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3698,19 +3698,20 @@ static void swap_ptr(void *l, void *r)
 	swap(*lp, *rp);
 }
 
+MIN_HEAP(struct perf_event *, perf_event_min_heap);
+
 static const struct min_heap_callbacks perf_min_heap = {
-	.elem_size = sizeof(struct perf_event *),
 	.less = perf_less_group_idx,
 	.swp = swap_ptr,
 };
 
-static void __heap_add(struct min_heap *heap, struct perf_event *event)
+static void __heap_add(struct perf_event_min_heap *heap, struct perf_event *event)
 {
-	struct perf_event **itrs = heap->data;
+	struct perf_event **itrs = heap->heap.data;
 
 	if (event) {
-		itrs[heap->nr] = event;
-		heap->nr++;
+		itrs[heap->heap.nr] = event;
+		heap->heap.nr++;
 	}
 }
 
@@ -3738,7 +3739,7 @@ static noinline int visit_groups_merge(struct perf_event_context *ctx,
 	struct perf_cpu_context *cpuctx = NULL;
 	/* Space for per CPU and/or any CPU event iterators. */
 	struct perf_event *itrs[2];
-	struct min_heap event_heap;
+	struct perf_event_min_heap event_heap;
 	struct perf_event **evt;
 	int ret;
 
@@ -3747,11 +3748,9 @@ static noinline int visit_groups_merge(struct perf_event_context *ctx,
 
 	if (!ctx->task) {
 		cpuctx = this_cpu_ptr(&perf_cpu_context);
-		event_heap = (struct min_heap){
-			.data = cpuctx->heap,
-			.nr = 0,
-			.size = cpuctx->heap_size,
-		};
+		event_heap.heap.data = cpuctx->heap;
+		event_heap.heap.nr = 0;
+		event_heap.heap.size = cpuctx->heap_size;
 
 		lockdep_assert_held(&cpuctx->ctx.lock);
 
@@ -3760,15 +3759,13 @@ static noinline int visit_groups_merge(struct perf_event_context *ctx,
 			css = &cpuctx->cgrp->css;
 #endif
 	} else {
-		event_heap = (struct min_heap){
-			.data = itrs,
-			.nr = 0,
-			.size = ARRAY_SIZE(itrs),
-		};
+		event_heap.heap.data = itrs;
+		event_heap.heap.nr = 0;
+		event_heap.heap.size = ARRAY_SIZE(itrs);
 		/* Events not within a CPU context may be on any CPU. */
 		__heap_add(&event_heap, perf_event_groups_first(groups, -1, pmu, NULL));
 	}
-	evt = event_heap.data;
+	evt = event_heap.heap.data;
 
 	__heap_add(&event_heap, perf_event_groups_first(groups, cpu, pmu, NULL));
 
@@ -3777,14 +3774,14 @@ static noinline int visit_groups_merge(struct perf_event_context *ctx,
 		__heap_add(&event_heap, perf_event_groups_first(groups, cpu, pmu, css->cgroup));
 #endif
 
-	if (event_heap.nr) {
+	if (event_heap.heap.nr) {
 		__link_epc((*evt)->pmu_ctx);
 		perf_assert_pmu_disabled((*evt)->pmu_ctx->pmu);
 	}
 
 	min_heapify_all(&event_heap, &perf_min_heap);
 
-	while (event_heap.nr) {
+	while (event_heap.heap.nr) {
 		ret = func(*evt, data);
 		if (ret)
 			return ret;
diff --git a/lib/test_min_heap.c b/lib/test_min_heap.c
index 7b01b4387cfb..af2e446034d8 100644
--- a/lib/test_min_heap.c
+++ b/lib/test_min_heap.c
@@ -11,6 +11,8 @@
 #include <linux/printk.h>
 #include <linux/random.h>
 
+MIN_HEAP(int, min_heap_test);
+
 static __init bool less_than(const void *lhs, const void *rhs)
 {
 	return *(int *)lhs < *(int *)rhs;
@@ -30,16 +32,16 @@ static __init void swap_ints(void *lhs, void *rhs)
 }
 
 static __init int pop_verify_heap(bool min_heap,
-				struct min_heap *heap,
+				struct min_heap_test *heap,
 				const struct min_heap_callbacks *funcs)
 {
-	int *values = heap->data;
+	int *values = heap->heap.data;
 	int err = 0;
 	int last;
 
 	last = values[0];
 	min_heap_pop(heap, funcs);
-	while (heap->nr > 0) {
+	while (heap->heap.nr > 0) {
 		if (min_heap) {
 			if (last > values[0]) {
 				pr_err("error: expected %d <= %d\n", last,
@@ -63,13 +65,12 @@ 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_heap heap = {
-		.data = values,
-		.nr = ARRAY_SIZE(values),
-		.size =  ARRAY_SIZE(values),
-	};
+	struct min_heap_test heap;
+
+	heap.heap.data = values;
+	heap.heap.nr = ARRAY_SIZE(values);
+	heap.heap.size =  ARRAY_SIZE(values);
 	struct min_heap_callbacks funcs = {
-		.elem_size = sizeof(int),
 		.less = min_heap ? less_than : greater_than,
 		.swp = swap_ints,
 	};
@@ -81,8 +82,8 @@ static __init int test_heapify_all(bool min_heap)
 
 
 	/* Test with randomly generated values. */
-	heap.nr = ARRAY_SIZE(values);
-	for (i = 0; i < heap.nr; i++)
+	heap.heap.nr = ARRAY_SIZE(values);
+	for (i = 0; i < heap.heap.nr; i++)
 		values[i] = get_random_u32();
 
 	min_heapify_all(&heap, &funcs);
@@ -96,13 +97,12 @@ 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_heap heap = {
-		.data = values,
-		.nr = 0,
-		.size =  ARRAY_SIZE(values),
-	};
+	struct min_heap_test heap;
+
+	heap.heap.data = values;
+	heap.heap.nr = 0;
+	heap.heap.size =  ARRAY_SIZE(values);
 	struct min_heap_callbacks funcs = {
-		.elem_size = sizeof(int),
 		.less = min_heap ? less_than : greater_than,
 		.swp = swap_ints,
 	};
@@ -115,7 +115,7 @@ static __init int test_heap_push(bool min_heap)
 	err = pop_verify_heap(min_heap, &heap, &funcs);
 
 	/* Test with randomly generated values. */
-	while (heap.nr < heap.size) {
+	while (heap.heap.nr < heap.heap.size) {
 		temp = get_random_u32();
 		min_heap_push(&heap, &temp, &funcs);
 	}
@@ -129,13 +129,12 @@ 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_heap heap = {
-		.data = values,
-		.nr = 0,
-		.size =  ARRAY_SIZE(values),
-	};
+	struct min_heap_test heap;
+
+	heap.heap.data = values;
+	heap.heap.nr = 0;
+	heap.heap.size =  ARRAY_SIZE(values);
 	struct min_heap_callbacks funcs = {
-		.elem_size = sizeof(int),
 		.less = min_heap ? less_than : greater_than,
 		.swp = swap_ints,
 	};
@@ -152,7 +151,7 @@ static __init int test_heap_pop_push(bool min_heap)
 
 	err = pop_verify_heap(min_heap, &heap, &funcs);
 
-	heap.nr = 0;
+	heap.heap.nr = 0;
 	for (i = 0; i < ARRAY_SIZE(data); i++)
 		min_heap_push(&heap, &temp, &funcs);
 
-- 
2.34.1