Re: [PATCH v2 05/10] mm, hugetlb: fix and clean-up node iterationcode to alloc or free

[Michal Hocko]

On Mon 22-07-13 17:36:26, Joonsoo Kim wrote:
> Current node iteration code have a minor problem which do one more
> node rotation if we can't succeed to allocate. For example,
> if we start to allocate at node 0, we stop to iterate at node 0.
> Then we start to allocate at node 1 for next allocation.
> 
> I introduce new macros "for_each_node_mask_to_[alloc|free]" and
> fix and clean-up node iteration code to alloc or free.
> This makes code more understandable.

I don't know but it feels like you are trying to fix an awkward
interface with another one. Why hstate_next_node_to_alloc cannot simply
return MAX_NUMNODES once the loop is done and start from first_node next
time it is called? We wouldn't have the bug you are mentioning and you
do not need scary looking macros.
 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 83edd17..3ac0a6f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -752,33 +752,6 @@ static int hstate_next_node_to_alloc(struct hstate *h,
>  	return nid;
>  }
>  
> -static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> -{
> -	struct page *page;
> -	int start_nid;
> -	int next_nid;
> -	int ret = 0;
> -
> -	start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> -	next_nid = start_nid;
> -
> -	do {
> -		page = alloc_fresh_huge_page_node(h, next_nid);
> -		if (page) {
> -			ret = 1;
> -			break;
> -		}
> -		next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> -	} while (next_nid != start_nid);
> -
> -	if (ret)
> -		count_vm_event(HTLB_BUDDY_PGALLOC);
> -	else
> -		count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
> -
> -	return ret;
> -}
> -
>  /*
>   * helper for free_pool_huge_page() - return the previously saved
>   * node ["this node"] from which to free a huge page.  Advance the
> @@ -797,6 +770,40 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>  	return nid;
>  }
>  
> +#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask)		\
> +	for (nr_nodes = nodes_weight(*mask);				\
> +		nr_nodes > 0 &&						\
> +		((node = hstate_next_node_to_alloc(hs, mask)) || 1);	\
> +		nr_nodes--)
> +
> +#define for_each_node_mask_to_free(hs, nr_nodes, node, mask)		\
> +	for (nr_nodes = nodes_weight(*mask);				\
> +		nr_nodes > 0 &&						\
> +		((node = hstate_next_node_to_free(hs, mask)) || 1);	\
> +		nr_nodes--)
> +
> +static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> +{
> +	struct page *page;
> +	int nr_nodes, node;
> +	int ret = 0;
> +
> +	for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> +		page = alloc_fresh_huge_page_node(h, node);
> +		if (page) {
> +			ret = 1;
> +			break;
> +		}
> +	}
> +
> +	if (ret)
> +		count_vm_event(HTLB_BUDDY_PGALLOC);
> +	else
> +		count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
> +
> +	return ret;
> +}
> +
>  /*
>   * Free huge page from pool from next node to free.
>   * Attempt to keep persistent huge pages more or less
> @@ -806,36 +813,31 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>  static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
>  							 bool acct_surplus)
>  {
> -	int start_nid;
> -	int next_nid;
> +	int nr_nodes, node;
>  	int ret = 0;
>  
> -	start_nid = hstate_next_node_to_free(h, nodes_allowed);
> -	next_nid = start_nid;
> -
> -	do {
> +	for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
>  		/*
>  		 * If we're returning unused surplus pages, only examine
>  		 * nodes with surplus pages.
>  		 */
> -		if ((!acct_surplus || h->surplus_huge_pages_node[next_nid]) &&
> -		    !list_empty(&h->hugepage_freelists[next_nid])) {
> +		if ((!acct_surplus || h->surplus_huge_pages_node[node]) &&
> +		    !list_empty(&h->hugepage_freelists[node])) {
>  			struct page *page =
> -				list_entry(h->hugepage_freelists[next_nid].next,
> +				list_entry(h->hugepage_freelists[node].next,
>  					  struct page, lru);
>  			list_del(&page->lru);
>  			h->free_huge_pages--;
> -			h->free_huge_pages_node[next_nid]--;
> +			h->free_huge_pages_node[node]--;
>  			if (acct_surplus) {
>  				h->surplus_huge_pages--;
> -				h->surplus_huge_pages_node[next_nid]--;
> +				h->surplus_huge_pages_node[node]--;
>  			}
>  			update_and_free_page(h, page);
>  			ret = 1;
>  			break;
>  		}
> -		next_nid = hstate_next_node_to_free(h, nodes_allowed);
> -	} while (next_nid != start_nid);
> +	}
>  
>  	return ret;
>  }
> @@ -1172,14 +1174,12 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>  int __weak alloc_bootmem_huge_page(struct hstate *h)
>  {
>  	struct huge_bootmem_page *m;
> -	int nr_nodes = nodes_weight(node_states[N_MEMORY]);
> +	int nr_nodes, node;
>  
> -	while (nr_nodes) {
> +	for_each_node_mask_to_alloc(h, nr_nodes, node, &node_states[N_MEMORY]) {
>  		void *addr;
>  
> -		addr = __alloc_bootmem_node_nopanic(
> -				NODE_DATA(hstate_next_node_to_alloc(h,
> -						&node_states[N_MEMORY])),
> +		addr = __alloc_bootmem_node_nopanic(NODE_DATA(node),
>  				huge_page_size(h), huge_page_size(h), 0);
>  
>  		if (addr) {
> @@ -1191,7 +1191,6 @@ int __weak alloc_bootmem_huge_page(struct hstate *h)
>  			m = addr;
>  			goto found;
>  		}
> -		nr_nodes--;
>  	}
>  	return 0;
>  
> @@ -1330,48 +1329,28 @@ static inline void try_to_free_low(struct hstate *h, unsigned long count,
>  static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
>  				int delta)
>  {
> -	int start_nid, next_nid;
> -	int ret = 0;
> +	int nr_nodes, node;
>  
>  	VM_BUG_ON(delta != -1 && delta != 1);
>  
> -	if (delta < 0)
> -		start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> -	else
> -		start_nid = hstate_next_node_to_free(h, nodes_allowed);
> -	next_nid = start_nid;
> -
> -	do {
> -		int nid = next_nid;
> -		if (delta < 0)  {
> -			/*
> -			 * To shrink on this node, there must be a surplus page
> -			 */
> -			if (!h->surplus_huge_pages_node[nid]) {
> -				next_nid = hstate_next_node_to_alloc(h,
> -								nodes_allowed);
> -				continue;
> -			}
> +	if (delta < 0) {
> +		for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> +			if (h->surplus_huge_pages_node[node])
> +				goto found;
>  		}
> -		if (delta > 0) {
> -			/*
> -			 * Surplus cannot exceed the total number of pages
> -			 */
> -			if (h->surplus_huge_pages_node[nid] >=
> -						h->nr_huge_pages_node[nid]) {
> -				next_nid = hstate_next_node_to_free(h,
> -								nodes_allowed);
> -				continue;
> -			}
> +	} else {
> +		for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
> +			if (h->surplus_huge_pages_node[node] <
> +					h->nr_huge_pages_node[node])
> +				goto found;
>  		}
> +	}
> +	return 0;
>  
> -		h->surplus_huge_pages += delta;
> -		h->surplus_huge_pages_node[nid] += delta;
> -		ret = 1;
> -		break;
> -	} while (next_nid != start_nid);
> -
> -	return ret;
> +found:
> +	h->surplus_huge_pages += delta;
> +	h->surplus_huge_pages_node[node] += delta;
> +	return 1;
>  }
>  
>  #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
> -- 
> 1.7.9.5
> 

-- 
Michal Hocko
SUSE Labs
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