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SubjectRe: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero
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On 3/27/20 3:01 PM, Wei Yang wrote:
> Since we always clear node_order before getting it, we can leverage
> compiler to do this instead of at run time.
>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
> mm/page_alloc.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dfcf2682ed40..49dd1f25c000 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5585,7 +5585,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
>
> static void build_zonelists(pg_data_t *pgdat)
> {
> - static int node_order[MAX_NUMNODES];
> + static int node_order[MAX_NUMNODES] = {0};


Looks wrong: now the single instance of node_order is initialized just once by
the compiler. And that means that only the first caller of this function
gets a zeroed node_order array...


> int node, load, nr_nodes = 0;
> nodemask_t used_mask = NODE_MASK_NONE;
> int local_node, prev_node;
> @@ -5595,7 +5595,6 @@ static void build_zonelists(pg_data_t *pgdat)
> load = nr_online_nodes;
> prev_node = local_node;
>
> - memset(node_order, 0, sizeof(node_order));

...and all subsequent callers are left with whatever debris is remaining in
node_order. So this is not good.

The reason that memset() was used here, is that there aren't many other ways
to get node_order zeroed, given that it is a statically defined variable.


> while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
> /*
> * We don't want to pressure a particular node.
>



thanks,
--
John Hubbard
NVIDIA

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