[PATCH v2 04/15] lib min_heap: Add type safe interface

From: Kuan-Wei Chiu
Date: Wed Mar 20 2024 - 10:55:56 EST

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@xxxxxxxxx>
Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
---
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