[dpdk-dev] [PATCH] malloc: fix rte_free run time in O(n) free blocks

[Sanford, Robert]

I haven't heard anything regarding this patch.
In general, how does your team keep track of outstanding patch requests or
RFCs?

Thanks,
Robert


>Here is our proposed patch:
>
>Lib rte_malloc stores free blocks in singly-linked lists.
>This results in O(n), i.e., poor performance when freeing memory
>to a heap that contains thousands of free blocks.
>
>A simple solution is to store free blocks on doubly-linked lists.
>- Space-wise, we add one new pointer to struct malloc_elem.
> This does not affect its size, since it is cache-aligned and
> currently has room for another pointer.
>- We perform all free list adds and deletes in functions
> malloc_elem_add_to_free_list and remove_from_free_list.
>- We clean up internal malloc functions that push or
> return pointers to previous blocks in the free list.
>
>
>---
> lib/librte_malloc/malloc_elem.c |   82
>+++++++++++++++++++++++---------------
> lib/librte_malloc/malloc_elem.h |    6 ++-
> lib/librte_malloc/malloc_heap.c |   19 +++------
> 3 files changed, 60 insertions(+), 47 deletions(-)
>
>diff --git a/lib/librte_malloc/malloc_elem.c
>b/lib/librte_malloc/malloc_elem.c
>index f0da640..9a14e23 100644
>--- a/lib/librte_malloc/malloc_elem.c
>+++ b/lib/librte_malloc/malloc_elem.c
>@@ -60,7 +60,7 @@ malloc_elem_init(struct malloc_elem *elem,
> {
> 	elem->heap = heap;
> 	elem->mz = mz;
>-	elem->prev = elem->next_free = NULL;
>+	elem->prev = elem->next_free = elem->prev_free = NULL;
> 	elem->state = ELEM_FREE;
> 	elem->size = size;
> 	elem->pad = 0;
>@@ -125,14 +125,58 @@ split_elem(struct malloc_elem *elem, struct
>malloc_elem *split_pt)
> }
> 
> /*
>+ * Add the specified element to its heap's free list.
>+ */
>+void
>+malloc_elem_add_to_free_list(struct malloc_elem *elem)
>+{
>+	elem->state = ELEM_FREE;
>+	elem->prev_free = NULL;
>+	if (!!(elem->next_free = elem->heap->free_head))
>+		elem->next_free->prev_free = elem;
>+	elem->heap->free_head = elem;
>+}
>+
>+/*
>+ * Remove the specified element from its heap's free list.
>+ */
>+static inline void
>+remove_from_free_list(struct malloc_elem *elem)
>+{
>+	struct malloc_elem *next_free_elem = elem->next_free;
>+	struct malloc_elem *prev_free_elem = elem->prev_free;
>+
>+	if (!!next_free_elem) {
>+#ifdef RTE_LIBRTE_MALLOC_DEBUG
>+		RTE_VERIFY(next_free_elem->prev_free == elem);
>+#endif
>+		next_free_elem->prev_free = prev_free_elem;
>+	}
>+
>+	if (!!prev_free_elem) {
>+#ifdef RTE_LIBRTE_MALLOC_DEBUG
>+		RTE_VERIFY(prev_free_elem->next_free == elem);
>+#endif
>+		prev_free_elem->next_free = next_free_elem;
>+	}
>+	else {
>+		struct malloc_heap *heap = elem->heap;
>+
>+#ifdef RTE_LIBRTE_MALLOC_DEBUG
>+		RTE_VERIFY(heap->free_head == elem);
>+#endif
>+		heap->free_head = next_free_elem;
>+	}
>+}
>+
>+/*
>  * reserve a block of data in an existing malloc_elem. If the malloc_elem
>  * is much larger than the data block requested, we split the element in
>two.
>  * This function is only called from malloc_heap_alloc so parameter
>checking
>  * is not done here, as it's done there previously.
>  */
> struct malloc_elem *
>-malloc_elem_alloc(struct malloc_elem *elem, size_t size,
>-		unsigned align, struct malloc_elem *prev_free)
>+malloc_elem_alloc(struct malloc_elem *elem, size_t size, unsigned align)
> {
> 	struct malloc_elem *new_elem = elem_start_pt(elem, size, align);
> 	const unsigned old_elem_size = (uintptr_t)new_elem - (uintptr_t)elem;
>@@ -151,10 +195,7 @@ malloc_elem_alloc(struct malloc_elem *elem, size_t
>size,
> 			set_header(new_elem);
> 		}
> 		/* remove element from free list */
>-		if (prev_free == NULL)
>-			elem->heap->free_head = elem->next_free;
>-		else
>-			prev_free->next_free = elem->next_free;
>+		remove_from_free_list(elem);
> 
> 		return new_elem;
> 	}
>@@ -182,25 +223,6 @@ join_elem(struct malloc_elem *elem1, struct
>malloc_elem *elem2)
> }
> 
> /*
>- * scan the free list, and remove the request element from that
>- * free list. (Free list to scan is got from heap pointer in element)
>- */
>-static inline void
>-remove_from_free_list(struct malloc_elem *elem)
>-{
>-	if (elem == elem->heap->free_head)
>-		elem->heap->free_head = elem->next_free;
>-	else{
>-		struct malloc_elem *prev_free = elem->heap->free_head;
>-		while (prev_free && prev_free->next_free != elem)
>-			prev_free = prev_free->next_free;
>-		if (!prev_free)
>-			rte_panic("Corrupted free list\n");
>-		prev_free->next_free = elem->next_free;
>-	}
>-}
>-
>-/*
>  * free a malloc_elem block by adding it to the free list. If the
>  * blocks either immediately before or immediately after newly freed
>block
>  * are also free, the blocks are merged together.
>@@ -226,9 +248,7 @@ malloc_elem_free(struct malloc_elem *elem)
> 		join_elem(elem->prev, elem);
> 	/* otherwise add ourselves to the free list */
> 	else {
>-		elem->next_free = elem->heap->free_head;
>-		elem->heap->free_head = elem;
>-		elem->state = ELEM_FREE;
>+		malloc_elem_add_to_free_list(elem);
> 		elem->pad = 0;
> 	}
> 	/* decrease heap's count of allocated elements */
>@@ -269,9 +289,7 @@ malloc_elem_resize(struct malloc_elem *elem, size_t
>size)
> 		struct malloc_elem *split_pt = RTE_PTR_ADD(elem, new_size);
> 		split_pt = RTE_PTR_ALIGN_CEIL(split_pt, CACHE_LINE_SIZE);
> 		split_elem(elem, split_pt);
>-		split_pt->state = ELEM_FREE;
>-		split_pt->next_free = elem->heap->free_head;
>-		elem->heap->free_head = split_pt;
>+		malloc_elem_add_to_free_list(split_pt);
> 	}
> 	rte_spinlock_unlock(&elem->heap->lock);
> 	return 0;
>diff --git a/lib/librte_malloc/malloc_elem.h
>b/lib/librte_malloc/malloc_elem.h
>index eadecf9..6d2d7db 100644
>--- a/lib/librte_malloc/malloc_elem.h
>+++ b/lib/librte_malloc/malloc_elem.h
>@@ -47,6 +47,7 @@ struct malloc_elem {
> 	struct malloc_heap *heap;
> 	struct malloc_elem *volatile prev;      /* points to prev elem in
>memzone */
> 	struct malloc_elem *volatile next_free; /* to make list of free elements
>*/
>+	struct malloc_elem *volatile prev_free; /* make free list doubly-linked
>*/
> 	const struct rte_memzone *mz;
> 	volatile enum elem_state state;
> 	uint32_t pad;
>@@ -156,8 +157,7 @@ malloc_elem_can_hold(struct malloc_elem *elem, size_t
>size, unsigned align);
>  * is much larger than the data block requested, we split the element in
>two.
>  */
> struct malloc_elem *
>-malloc_elem_alloc(struct malloc_elem *elem, size_t size,
>-		unsigned align, struct malloc_elem *prev_free);
>+malloc_elem_alloc(struct malloc_elem *elem, size_t size, unsigned align);
> 
> /*
>  * free a malloc_elem block by adding it to the free list. If the
>@@ -174,4 +174,6 @@ malloc_elem_free(struct malloc_elem *elem);
> int
> malloc_elem_resize(struct malloc_elem *elem, size_t size);
> 
>+void malloc_elem_add_to_free_list(struct malloc_elem *elem);
>+
> #endif /* MALLOC_ELEM_H_ */
>diff --git a/lib/librte_malloc/malloc_heap.c
>b/lib/librte_malloc/malloc_heap.c
>index f4a0294..bc146e1 100644
>--- a/lib/librte_malloc/malloc_heap.c
>+++ b/lib/librte_malloc/malloc_heap.c
>@@ -112,9 +112,8 @@ malloc_heap_add_memzone(struct malloc_heap *heap,
>size_t size, unsigned align)
> 	const unsigned elem_size = (uintptr_t)end_elem - (uintptr_t)start_elem;
> 	malloc_elem_init(start_elem, heap, mz, elem_size);
> 	malloc_elem_mkend(end_elem, start_elem);
>+	malloc_elem_add_to_free_list(start_elem);
> 
>-	start_elem->next_free = heap->free_head;
>-	heap->free_head = start_elem;
> 	/* increase heap total size by size of new memzone */
> 	heap->total_size+=mz_size - MALLOC_ELEM_OVERHEAD;
> 	return 0;
>@@ -160,27 +159,22 @@ malloc_heap_init(struct malloc_heap *heap)
>  * (to make removing the element from the free list faster).
>  */
> static struct malloc_elem *
>-find_suitable_element(struct malloc_heap *heap, size_t size,
>-		unsigned align, struct malloc_elem **prev)
>+find_suitable_element(struct malloc_heap *heap, size_t size, unsigned
>align)
> {
>-	struct malloc_elem *elem, *min_elem, *min_prev;
>+	struct malloc_elem *elem, *min_elem;
> 	size_t min_sz;
> 
> 	elem = heap->free_head;
> 	min_elem = NULL;
>-	min_prev = NULL;
> 	min_sz = (size_t) SIZE_MAX;
>-	*prev = NULL;
> 
> 	while(elem){
> 		if (malloc_elem_can_hold(elem, size, align)) {
> 			if (min_sz > elem->size) {
> 				min_elem = elem;
>-				*prev = min_prev;
> 				min_sz = elem->size;
> 			}
> 		}
>-		min_prev = elem;
> 		elem = elem->next_free;
> 	}
> 	return (min_elem);
>@@ -202,15 +196,14 @@ malloc_heap_alloc(struct malloc_heap *heap,
> 	size = CACHE_LINE_ROUNDUP(size);
> 	align = CACHE_LINE_ROUNDUP(align);
> 	rte_spinlock_lock(&heap->lock);
>-	struct malloc_elem *prev, *elem = find_suitable_element(heap,
>-			size, align, &prev);
>+	struct malloc_elem *elem = find_suitable_element(heap, size, align);
> 	if (elem == NULL){
> 		if ((malloc_heap_add_memzone(heap, size, align)) == 0)
>-			elem = find_suitable_element(heap, size, align, &prev);
>+			elem = find_suitable_element(heap, size, align);
> 	}
> 
> 	if (elem != NULL){
>-		elem = malloc_elem_alloc(elem, size, align, prev);
>+		elem = malloc_elem_alloc(elem, size, align);
> 		/* increase heap's count of allocated elements */
> 		heap->alloc_count++;
> 	}
>-- 
>1.7.1
>
>Signed-off-by: Robert Sanford <rsanford at akamai.com>
>