linux-kernel - Re: [PATCH 1/2] mm/page_alloc.c: leverage compiler to zero out used

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Date:   Fri, 27 Mar 2020 10:32:45 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/page_alloc.c: leverage compiler to zero out
 used_mask

On 26.03.20 23:24, Wei Yang wrote:
> Since we always clear used_mask before getting node order, we can
> leverage compiler to do this instead of at run time.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...il.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 0e823bca3f2f..2144b6ceb119 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5587,14 +5587,13 @@ static void build_zonelists(pg_data_t *pgdat)
>  {
>  	static int node_order[MAX_NUMNODES];
>  	int node, load, nr_nodes = 0;
> -	nodemask_t used_mask;
> +	nodemask_t used_mask = {.bits = {0}};
>  	int local_node, prev_node;
>  
>  	/* NUMA-aware ordering of nodes */
>  	local_node = pgdat->node_id;
>  	load = nr_online_nodes;
>  	prev_node = local_node;
> -	nodes_clear(used_mask);
>  
>  	memset(node_order, 0, sizeof(node_order));
>  	while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
> 

t480s: ~/git/linux default_online_type $ git grep "nodemask_t " | grep "="
arch/x86/mm/numa.c:     nodemask_t reserved_nodemask = NODE_MASK_NONE;
arch/x86/mm/numa_emulation.c:   nodemask_t physnode_mask = numa_nodes_parsed;
arch/x86/mm/numa_emulation.c:   nodemask_t physnode_mask = numa_nodes_parsed;
arch/x86/mm/numa_emulation.c:           nodemask_t physnode_mask = numa_nodes_parsed;
drivers/acpi/numa/srat.c:static nodemask_t nodes_found_map = NODE_MASK_NONE;
kernel/irq/affinity.c:  nodemask_t nodemsk = NODE_MASK_NONE;
kernel/sched/fair.c:            nodemask_t max_group = NODE_MASK_NONE;
mm/memory_hotplug.c:    nodemask_t nmask = node_states[N_MEMORY];
mm/mempolicy.c:         nodemask_t mems = cpuset_mems_allowed(current);
mm/mempolicy.c: nodemask_t nodes = NODE_MASK_NONE;
mm/oom_kill.c:  const nodemask_t *mask = oc->nodemask;
mm/page_alloc.c:nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
mm/page_alloc.c:        nodemask_t saved_node_state = node_states[N_MEMORY];

Should this be NODE_MASK_NONE?

-- 
Thanks,

David / dhildenb