linux-kernel - Re: [PATCH] signal: reorder struct sighand

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Message-ID: <20190504233302.GT29835@dhcp22.suse.cz>
Date:   Sat, 4 May 2019 19:33:02 -0400
From:   Michal Hocko <mhocko@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] signal: reorder struct sighand_struct

CCing Oleg.

On Fri 03-05-19 22:28:00, Alexey Dobriyan wrote:
[...]
> add/remove: 0/0 grow/shrink: 8/68 up/down: 49/-1147 (-1098)
[...]
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -15,10 +15,10 @@
>   */
>  
>  struct sighand_struct {
> -	refcount_t		count;
> -	struct k_sigaction	action[_NSIG];
>  	spinlock_t		siglock;
> +	refcount_t		count;
>  	wait_queue_head_t	signalfd_wqh;
> +	struct k_sigaction	action[_NSIG];
>  };

Is it possible that this would cause false sharing of the cache line
that would have performance implications now?

-- 
Michal Hocko
SUSE Labs