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

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Message-ID: <20200326223604.GP20941@ziepe.ca>
Date:   Thu, 26 Mar 2020 19:36:04 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     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 Thu, Mar 26, 2020 at 10:24:44PM +0000, 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
> +++ 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}};

If this style is to be done it should just be '= {}';

This case demonstrates why the popular '= {0}' idiom is not such a
good idea, as it only works if the first member is an integral type.

Jason