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 13:21:58 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Wei Yang <richard.weiyang@...il.com>, akpm@...ux-foundation.org,
        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 Fri, Mar 27, 2020 at 10:32:45AM +0100, David Hildenbrand wrote:
>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, this is gcc extension. Learn something new.

I would update this in v2.

>
>-- 
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me