Re: [PATCH 4/9] mm, hugetlb: fix and clean-up node iteration code to alloc or free

Aneesh Kumar K.V
2013-07-15T14:27:48Z

Joonsoo Kim <iamjoonsoo.kim@lge.com> writes:

> 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.

Can you explain the problem in a bit more detail

>
> 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 found the existing code more readable. Obviously I haven't yet figured
out the problem you have observed with the code.

> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0067cf4..a838e6b 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 +770,42 @@ 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), \
> + node = hstate_next_node_to_alloc(hs, 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), \
> + node = hstate_next_node_to_free(hs, 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) {

This check for nodes_weight and fail right ? (nr_nodes == 0). That is
not the case with the existing code. It will allocate from
h->next_nid_to_alloc. Is that ok ?

> + 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;
> +}
> +

-aneesh