Re: [PATCH 1/11] hugetlb: rework hstate_next_node_* functions

[David Rientjes <rientjes@google.com>]

On Tue, 15 Sep 2009, Lee Schermerhorn wrote:

> Index: linux-2.6.31-mmotm-090914-0157/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.31-mmotm-090914-0157.orig/mm/hugetlb.c	2009-09-15 13:23:01.000000000 -0400
> +++ linux-2.6.31-mmotm-090914-0157/mm/hugetlb.c	2009-09-15 13:42:14.000000000 -0400
> @@ -622,6 +622,20 @@ static struct page *alloc_fresh_huge_pag
>  }
>  
>  /*
> + * common helper function for hstate_next_node_to_{alloc|free}.
> + * return next node in node_online_map, wrapping at end.
> + */
> +static int next_node_allowed(int nid)
> +{
> +	nid = next_node(nid, node_online_map);
> +	if (nid == MAX_NUMNODES)
> +		nid = first_node(node_online_map);
> +	VM_BUG_ON(nid >= MAX_NUMNODES);
> +
> +	return nid;
> +}
> +
> +/*
>   * Use a helper variable to find the next node and then
>   * copy it back to next_nid_to_alloc afterwards:
>   * otherwise there's a window in which a racer might
> @@ -634,12 +648,12 @@ static struct page *alloc_fresh_huge_pag
>   */
>  static int hstate_next_node_to_alloc(struct hstate *h)
>  {
> -	int next_nid;
> -	next_nid = next_node(h->next_nid_to_alloc, node_online_map);
> -	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(node_online_map);
> +	int nid, next_nid;
> +
> +	nid = h->next_nid_to_alloc;
> +	next_nid = next_node_allowed(nid);
>  	h->next_nid_to_alloc = next_nid;
> -	return next_nid;
> +	return nid;
>  }
>  
>  static int alloc_fresh_huge_page(struct hstate *h)

I thought you had refactored this to drop next_nid entirely since gcc 
optimizes it away?

> @@ -649,15 +663,17 @@ static int alloc_fresh_huge_page(struct
>  	int next_nid;
>  	int ret = 0;
>  
> -	start_nid = h->next_nid_to_alloc;
> +	start_nid = hstate_next_node_to_alloc(h);
>  	next_nid = start_nid;
>  
>  	do {
>  		page = alloc_fresh_huge_page_node(h, next_nid);
> -		if (page)
> +		if (page) {
>  			ret = 1;
> +			break;
> +		}
>  		next_nid = hstate_next_node_to_alloc(h);
> -	} while (!page && next_nid != start_nid);
> +	} while (next_nid != start_nid);
>  
>  	if (ret)
>  		count_vm_event(HTLB_BUDDY_PGALLOC);
> @@ -668,17 +684,19 @@ static int alloc_fresh_huge_page(struct
>  }
>  
>  /*
> - * helper for free_pool_huge_page() - find next node
> - * from which to free a huge page
> + * helper for free_pool_huge_page() - return the next node
> + * from which to free a huge page.  Advance the next node id
> + * whether or not we find a free huge page to free so that the
> + * next attempt to free addresses the next node.
>   */
>  static int hstate_next_node_to_free(struct hstate *h)
>  {
> -	int next_nid;
> -	next_nid = next_node(h->next_nid_to_free, node_online_map);
> -	if (next_nid == MAX_NUMNODES)
> -		next_nid = first_node(node_online_map);
> +	int nid, next_nid;
> +
> +	nid = h->next_nid_to_free;
> +	next_nid = next_node_allowed(nid);
>  	h->next_nid_to_free = next_nid;
> -	return next_nid;
> +	return nid;
>  }
>  
>  /*

Ditto for next_nid.

> @@ -693,7 +711,7 @@ static int free_pool_huge_page(struct hs
>  	int next_nid;
>  	int ret = 0;
>  
> -	start_nid = h->next_nid_to_free;
> +	start_nid = hstate_next_node_to_free(h);
>  	next_nid = start_nid;
>  
>  	do {
> @@ -715,9 +733,10 @@ static int free_pool_huge_page(struct hs
>  			}
>  			update_and_free_page(h, page);
>  			ret = 1;
> +			break;
>  		}
>  		next_nid = hstate_next_node_to_free(h);
> -	} while (!ret && next_nid != start_nid);
> +	} while (next_nid != start_nid);
>  
>  	return ret;
>  }
> @@ -1028,10 +1047,9 @@ int __weak alloc_bootmem_huge_page(struc
>  		void *addr;
>  
>  		addr = __alloc_bootmem_node_nopanic(
> -				NODE_DATA(h->next_nid_to_alloc),
> +				NODE_DATA(hstate_next_node_to_alloc(h)),
>  				huge_page_size(h), huge_page_size(h), 0);
>  
> -		hstate_next_node_to_alloc(h);
>  		if (addr) {
>  			/*
>  			 * Use the beginning of the huge page to store the

Shouldn't that panic if hstate_next_node_to_alloc() returns a memoryless 
node since it uses node_online_map?

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