linux-kernel - Re: [PATCH] uprobes: Re-order struct uprobe

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Message-Id: <20241103135548.0c19e1a1451e598c18d8c42f@kernel.org>
Date: Sun, 3 Nov 2024 13:55:48 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] uprobes: Re-order struct uprobe_task to save some space

On Fri,  1 Nov 2024 22:13:33 +0100
Christophe JAILLET <christophe.jaillet@...adoo.fr> wrote:

> On x86_64, with allmodconfig, struct uprobe_task is 72 bytes long, with a
> hole and some padding.
> 
> 	/* size: 72, cachelines: 2, members: 7 */
> 	/* sum members: 64, holes: 1, sum holes: 4 */
> 	/* padding: 4 */
> 	/* forced alignments: 1, forced holes: 1, sum forced holes: 4 */
> 	/* last cacheline: 8 bytes */
> 
> Reorder the structure to fill the hole and avoid the padding.
> 
> This way, the whole structure fits in a single cacheline and some memory is
> saved when it is allocated.
> 
> 	/* size: 64, cachelines: 1, members: 7 */
> 	/* forced alignments: 1 */
> 

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you!

> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> Compile tested only
> ---
>  include/linux/uprobes.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index dbaf04189548..c684a470477f 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -73,6 +73,9 @@ enum uprobe_task_state {
>  struct uprobe_task {
>  	enum uprobe_task_state		state;
>  
> +	unsigned int			depth;
> +	struct return_instance		*return_instances;
> +
>  	union {
>  		struct {
>  			struct arch_uprobe_task	autask;
> @@ -89,9 +92,6 @@ struct uprobe_task {
>  	unsigned long			xol_vaddr;
>  
>  	struct arch_uprobe              *auprobe;
> -
> -	struct return_instance		*return_instances;
> -	unsigned int			depth;
>  };
>  
>  struct return_consumer {
> -- 
> 2.47.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>