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

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Message-ID: <a9f541d0cedf421f765c77a1fb93d6a979778a88.1730495562.git.christophe.jaillet@wanadoo.fr>
Date: Fri,  1 Nov 2024 22:13:33 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Masami Hiramatsu <mhiramat@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH] uprobes: Re-order struct uprobe_task to save some space

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 */

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