linux-kernel - Re: [PATCH] mm: Outline copy

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Date:   Mon, 7 Feb 2022 12:40:02 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: Outline copy_overflow()

On Mon,  7 Feb 2022 11:55:18 +0100 Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> While building a small config with CONFIG_CC_OPTIMISE_FOR_SIZE,
> I ended up with more than 50 times the following function in vmlinux:
> 
> 	c00243bc <copy_overflow>:
> 	c00243bc:	94 21 ff f0 	stwu    r1,-16(r1)
> 	c00243c0:	7c 85 23 78 	mr      r5,r4
> 	c00243c4:	7c 64 1b 78 	mr      r4,r3
> 	c00243c8:	3c 60 c0 62 	lis     r3,-16286
> 	c00243cc:	7c 08 02 a6 	mflr    r0
> 	c00243d0:	38 63 5e e5 	addi    r3,r3,24293
> 	c00243d4:	90 01 00 14 	stw     r0,20(r1)
> 	c00243d8:	4b ff 82 45 	bl      c001c61c <__warn_printk>
> 	c00243dc:	0f e0 00 00 	twui    r0,0
> 	c00243e0:	80 01 00 14 	lwz     r0,20(r1)
> 	c00243e4:	38 21 00 10 	addi    r1,r1,16
> 	c00243e8:	7c 08 03 a6 	mtlr    r0
> 	c00243ec:	4e 80 00 20 	blr
> 
> That function being a non conditional warning on an error path,
> it is not worth inlining.
> 
> Outline it.

"uninline" is the conventional term for this.

> This reduces the size of vmlinux by almost 4kbytes.

Did you consider uninlining check_copy_size() instead?