Re: [PATCH 1/1] network memory allocator.

[Andrew Morton <akpm@osdl.org>]

On Mon, 14 Aug 2006 15:04:03 +0400
Evgeniy Polyakov <johnpol@2ka.mipt.ru> wrote:

> 
> Design of allocator allows to map all node's pages into userspace thus
> allows to have true zero-copy support for both sending and receiving
> dataflows.

If the pages can be order-1 or higher then they'll need to be compound
pages so that the kernel gets the page's refcounting correct if the user
tries to perform direct-io against them (get_user_pages()).

And compound pages use ->lru for internal metadata - see prep_compound_page().

> +static avl_t avl_node_id[NR_CPUS];
> +static struct avl_node **avl_node_array[NR_CPUS];
> +static struct list_head *avl_container_array[NR_CPUS];
> +static struct avl_node *avl_root[NR_CPUS];
> +static struct avl_free_list *avl_free_list_head[NR_CPUS];
> +static spinlock_t avl_free_lock[NR_CPUS];

There will be heaps of cacheline pingpong accessing these arrays.  I'd have
though that

static struct whatever {
	avl_t avl_node_id;
	struct avl_node **avl_node_array;
	struct list_head *avl_container_array;
	struct avl_node *avl_root;
	struct avl_free_list *avl_free_list_head;
	spinlock_t avl_free_lock;
} __cacheline_aligned_in_smp whatevers[NR_CPUS];

would be better.

> +typedef unsigned long value_t;
> +typedef u16 avl_t;

Do we really need the typedefs?

If so, these have too generic names for globally-scoped identifiers.

> +static inline struct avl_node *avl_get_node(avl_t id, int cpu)
> +{
> +	avl_t idx, off;
> +
> +	if (id >= AVL_NODE_NUM)
> +		return NULL;
> +	
> +	idx = id/AVL_NODES_ON_PAGE;
> +	off = id%AVL_NODES_ON_PAGE;
> +
> +	return &(avl_node_array[cpu][idx][off]);
> +}

Too big to inline.

> +static inline struct avl_node *avl_get_node_ptr(unsigned long ptr)
> +{
> +	struct page *page = virt_to_page(ptr);
> +	struct avl_node *node = (struct avl_node *)(page->lru.next);
> +
> +	return node;
> +}

Probably OK.

> +static inline void avl_set_node_ptr(unsigned long ptr, struct avl_node *node, int order)
> +{
> +	int nr_pages = 1<<order, i;
> +	struct page *page = virt_to_page(ptr);
> +	
> +	for (i=0; i<nr_pages; ++i) {
> +		page->lru.next = (void *)node;
> +		page++;
> +	}
> +}

Too big

> +static inline int avl_get_cpu_ptr(unsigned long ptr)
> +{
> +	struct page *page = virt_to_page(ptr);
> +	int cpu = (int)(unsigned long)(page->lru.prev);
> +
> +	return cpu;
> +}

Too big

> +static inline void avl_set_cpu_ptr(unsigned long ptr, int cpu, int order)
> +{
> +	int nr_pages = 1<<order, i;
> +	struct page *page = virt_to_page(ptr);
> +			
> +	for (i=0; i<nr_pages; ++i) {
> +		page->lru.prev = (void *)(unsigned long)cpu;
> +		page++;
> +	}
> +}

Too big

> +static inline enum avl_balance avl_compare(struct avl_node *a, struct avl_node *b)
> +{
> +	if (a->value == b->value)
> +		return AVL_BALANCED;
> +	else if (a->value > b->value)
> +		return AVL_RIGHT;
> +	else
> +		return AVL_LEFT;
> +}

Might be too big.

> +static inline void avl_set_left(struct avl_node *node, avl_t val)
> +{
> +	node->left = val;
> +}
> +
> +static inline void avl_set_right(struct avl_node *node, avl_t val)
> +{
> +	node->right = val;
> +}
> +
> +static inline void avl_set_parent(struct avl_node *node, avl_t val)
> +{
> +	node->parent = val;
> +}

Not too big ;)

> +static inline void avl_rotate_complete(struct avl_node *parent, struct avl_node *node, int cpu)
> +{
> +	avl_set_parent(node, parent->parent);
> +	if (parent->parent != AVL_NODE_EMPTY) {
> +		if (parent->pos == AVL_RIGHT)
> +			avl_set_right(avl_get_node(parent->parent, cpu), node->id);
> +		else
> +			avl_set_left(avl_get_node(parent->parent, cpu), node->id);
> +	}
> +	avl_set_parent(parent, node->id);
> +}
> +
> +static inline void avl_ll(struct avl_node *node, int cpu)
> +{
> +	struct avl_node *parent = avl_get_node(node->parent, cpu);
> +	struct avl_node *left = avl_get_node(node->left, cpu);
> +	
> +	avl_rotate_complete(parent, node, cpu);
> +	avl_set_left(node, parent->id);
> +	node->pos = parent->pos;
> +	parent->pos = AVL_LEFT;
> +	if (!left) {
> +		avl_set_right(parent, AVL_NODE_EMPTY);
> +	} else {
> +		avl_set_parent(left, parent->id);
> +		left->pos = AVL_RIGHT;
> +		avl_set_right(parent, left->id);
> +	}
> +}
> +
> +static inline void avl_rr(struct avl_node *node, int cpu)
> +{
> +	struct avl_node *parent = avl_get_node(node->parent, cpu);
> +	struct avl_node *right = avl_get_node(node->right, cpu);
> +
> +	avl_rotate_complete(parent, node, cpu);
> +	avl_set_right(node, parent->id);
> +	node->pos = parent->pos;
> +	parent->pos = AVL_RIGHT;
> +	if (!right)
> +		avl_set_left(parent, AVL_NODE_EMPTY);
> +	else {
> +		avl_set_parent(right, parent->id);
> +		right->pos = AVL_LEFT;
> +		avl_set_left(parent, right->id);
> +	}
> +}
> +
> +static inline void avl_rl_balance(struct avl_node *node, int cpu)
> +{
> +	avl_rr(node, cpu);
> +	avl_ll(node, cpu);
> +}
> +
> +static inline void avl_lr_balance(struct avl_node *node, int cpu)
> +{
> +	avl_ll(node, cpu);
> +	avl_rr(node, cpu);
> +}
> +
> +static inline void avl_balance_single(struct avl_node *node, struct avl_node *parent)
> +{
> +	node->balance = parent->balance = AVL_BALANCED;
> +}
> +
> +static inline void avl_ll_balance(struct avl_node *node, int cpu)
> +{
> +	struct avl_node *parent = avl_get_node(node->parent, cpu);
> +
> +	avl_ll(node, cpu);
> +	avl_balance_single(node, parent);
> +}
> +
> +static inline void avl_rr_balance(struct avl_node *node, int cpu)
> +{
> +	struct avl_node *parent = avl_get_node(node->parent, cpu);
> +
> +	avl_rr(node, cpu);
> +	avl_balance_single(node, parent);
> +}

All way too big.

(Yes, avl_rr_balance() has a single callsite, as does avl_ll_balance(), but
they each have separate copies of the very large avl_rr())

> +	/*
> +	 * NTA steals pages and never return them back to the system.
> +	 */

That's the only code comment in this entire 882-line file?

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