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Date: Wed, 20 Mar 2024 16:56:57 -0400
From: Kent Overstreet <kent.overstreet@linux.dev>
To: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: colyli@suse.de, msakai@redhat.com, peterz@infradead.org, 
	mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, akpm@linux-foundation.org, 
	bfoster@redhat.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, 
	jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, 
	jserv@ccns.ncku.edu.tw, dm-devel@lists.linux.dev, linux-bcache@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-bcachefs@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: [PATCH v2 04/15] lib min_heap: Add type safe interface
Message-ID: <iz6wl3twuc72txd4ifxy73bbbfijo3ecy7izw3drsmcb2payeu@b2dusfoqobgu>
References: <20240320145417.336208-1-visitorckw@gmail.com>
 <20240320145417.336208-5-visitorckw@gmail.com>
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In-Reply-To: <20240320145417.336208-5-visitorckw@gmail.com>

On Wed, Mar 20, 2024 at 10:54:06PM +0800, Kuan-Wei Chiu wrote:
> 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.

let's avoid the heap->heap.nr - darray (fs/bcachefs/darray.h) has a
trick for that. All heaps have the same memory layout, so we can just
cast to a void pointer heap to get something the C code can use.

> 
> Link: https://lkml.kernel.org/ioyfizrzq7w7mjrqcadtzsfgpuntowtjdw5pgn4qhvsdp4mqqg@nrlek5vmisbu
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> Reviewed-by: Ian Rogers <irogers@google.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
>