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SubjectRe: [PATCH] Add nid sanity on alloc_pages_node
On Thu, 12 Jul 2007, Andrew Morton wrote:
>
> It'd be much better to fix the race within alloc_fresh_huge_page(). That
> function is pretty pathetic.
>
> Something like this?
>
> --- a/mm/hugetlb.c~a
> +++ a/mm/hugetlb.c
> @@ -105,13 +105,20 @@ static void free_huge_page(struct page *
>
> static int alloc_fresh_huge_page(void)
> {
> - static int nid = 0;
> + static int prev_nid;
> + static DEFINE_SPINLOCK(nid_lock);
> struct page *page;
> - page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
> - HUGETLB_PAGE_ORDER);
> - nid = next_node(nid, node_online_map);
> + int nid;
> +
> + spin_lock(&nid_lock);
> + nid = next_node(prev_nid, node_online_map);
> if (nid == MAX_NUMNODES)
> nid = first_node(node_online_map);
> + prev_nid = nid;
> + spin_unlock(&nid_lock);
> +
> + page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
> + HUGETLB_PAGE_ORDER);
> if (page) {
> set_compound_page_dtor(page, free_huge_page);
> spin_lock(&hugetlb_lock);

Now that it's gone into the tree, I look at it and wonder, does your
nid_lock really serve any purpose? We're just doing a simple assignment
to prev_nid, and it doesn't matter if occasionally two racers choose the
same node, and there's no protection here against a node being offlined
before the alloc_pages_node anyway (unsupported? I'm ignorant).

Hugh
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