On Mon, 5 Oct 2009, Lee Schermerhorn wrote:
> Index: linux-2.6.31-mmotm-090925-1435/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.31-mmotm-090925-1435.orig/mm/hugetlb.c 2009-09-28 10:12:20.000000000 -0400
> +++ linux-2.6.31-mmotm-090925-1435/mm/hugetlb.c 2009-09-30 11:41:36.000000000 -0400
> @@ -622,48 +622,56 @@ 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.
> + * common helper functions for hstate_next_node_to_{alloc|free}.
> + * We may have allocated or freed a huge page based on a different
> + * nodes_allowed previously, so h->next_node_to_{alloc|free} might
> + * be outside of *nodes_allowed. Ensure that we use an allowed
> + * node for alloc or free.
> */
> -static int next_node_allowed(int nid)
> +static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
> {
> - nid = next_node(nid, node_online_map);
> + nid = next_node(nid, *nodes_allowed);
> if (nid == MAX_NUMNODES)
> - nid = first_node(node_online_map);
> + nid = first_node(*nodes_allowed);
> VM_BUG_ON(nid >= MAX_NUMNODES);
>
> return nid;
> }
>
> +static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
> +{
> + if (!node_isset(nid, *nodes_allowed))
> + nid = next_node_allowed(nid, nodes_allowed);
> + 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
> - * pass invalid nid MAX_NUMNODES to alloc_pages_exact_node.
> - * But we don't need to use a spin_lock here: it really
> - * doesn't matter if occasionally a racer chooses the
> - * same nid as we do. Move nid forward in the mask even
> - * if we just successfully allocated a hugepage so that
> - * the next caller gets hugepages on the next node.
> + * returns the previously saved node ["this node"] from which to
> + * allocate a persistent huge page for the pool and advance the
> + * next node from which to allocate, handling wrap at end of node
> + * mask.
> */
> -static int hstate_next_node_to_alloc(struct hstate *h)
> +static int hstate_next_node_to_alloc(struct hstate *h,
> + nodemask_t *nodes_allowed)
> {
> - int nid, next_nid;
> + int nid;
> +
> + VM_BUG_ON(!nodes_allowed);
> +
> + nid = get_valid_node_allowed(h->next_nid_to_alloc, nodes_allowed);
> + h->next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
>
> - nid = h->next_nid_to_alloc;
> - next_nid = next_node_allowed(nid);
> - h->next_nid_to_alloc = next_nid;
> return nid;
> }
>
> -static int alloc_fresh_huge_page(struct hstate *h)
> +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);
> + start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> next_nid = start_nid;
>
> do {
> @@ -672,7 +680,7 @@ static int alloc_fresh_huge_page(struct
> ret = 1;
> break;
> }
> - next_nid = hstate_next_node_to_alloc(h);
> + next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
> } while (next_nid != start_nid);
>
> if (ret)
> @@ -684,18 +692,20 @@ static int alloc_fresh_huge_page(struct
> }
>
> /*
> - * 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.
> + * helper for free_pool_huge_page() - return the previously saved
> + * node ["this 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)
> +static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
> {
> - int nid, next_nid;
> + int nid;
> +
> + VM_BUG_ON(!nodes_allowed);
> +
> + nid = get_valid_node_allowed(h->next_nid_to_free, nodes_allowed);
> + h->next_nid_to_free = next_node_allowed(nid, nodes_allowed);
>
> - nid = h->next_nid_to_free;
> - next_nid = next_node_allowed(nid);
> - h->next_nid_to_free = next_nid;
> return nid;
> }
>
> @@ -705,13 +715,14 @@ static int hstate_next_node_to_free(stru
> * balanced over allowed nodes.
> * Called with hugetlb_lock locked.
> */
> -static int free_pool_huge_page(struct hstate *h, bool acct_surplus)
> +static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
> + bool acct_surplus)
> {
> int start_nid;
> int next_nid;
> int ret = 0;
>
> - start_nid = hstate_next_node_to_free(h);
> + start_nid = hstate_next_node_to_free(h, nodes_allowed);
> next_nid = start_nid;
>
> do {
> @@ -735,7 +746,7 @@ static int free_pool_huge_page(struct hs
> ret = 1;
> break;
> }
> - next_nid = hstate_next_node_to_free(h);
> + next_nid = hstate_next_node_to_free(h, nodes_allowed);
> } while (next_nid != start_nid);
>
> return ret;
> @@ -937,7 +948,7 @@ static void return_unused_surplus_pages(
> * on-line nodes for us and will handle the hstate accounting.
> */
> while (nr_pages--) {
> - if (!free_pool_huge_page(h, 1))
> + if (!free_pool_huge_page(h, &node_online_map, 1))
> break;
> }
> }
> @@ -1047,7 +1058,7 @@ int __weak alloc_bootmem_huge_page(struc
> void *addr;
>
> addr = __alloc_bootmem_node_nopanic(
> - NODE_DATA(hstate_next_node_to_alloc(h)),
> + NODE_DATA(hstate_next_node_to_alloc(h, NULL)),
> huge_page_size(h), huge_page_size(h), 0);
>
> if (addr) {
This will trigger the VM_BUG_ON() in hstate_next_node_to_alloc() so it
needs to be changed to &node_states[N_HIGH_MEMORY]. I'm wondering why it
didn't show up in testing; CONFIG_DEBUG_VM isn't enabled by default so
perhaps this hasn't had any hugepagez= coverage for hugepages of greater
than MAX_ORDER?
[ The VM_BUG_ON()'s in both hstate_next_node_to_alloc() and
hstate_next_node_to_free() are actually unnecessary since both will
quickly hit a node_isset() NULL pointer on the subsequent call to
get_valid_node_allowed() if it's true. ]
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