linux-kernel - Re: [PATCH] compiler_types: Introduce inline_for

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Message-Id: <20260118114724.cb7b7081109e88d4fa3c5836@linux-foundation.org>
Date: Sun, 18 Jan 2026 11:47:24 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: linux-kernel <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <eric.dumazet@...il.com>,
 Paolo Abeni <pabeni@...hat.com>, Nicolas Pitre <npitre@...libre.com>
Subject: Re: [PATCH] compiler_types: Introduce inline_for_performance

On Sun, 18 Jan 2026 15:24:48 +0000 Eric Dumazet <edumazet@...gle.com> wrote:

> inline keyword is often ignored by compilers.
> 
> We need something slightly stronger in networking fast paths
> but __always_inline is too strong.
> 
> Instead, generalize idea Nicolas used in commit d533cb2d2af4
> ("__arch_xprod64(): make __always_inline when optimizing for performance")
> 
> This will help CONFIG_CC_OPTIMIZE_FOR_SIZE=y users keeping
> their kernels small.

This is good.  __always_inline is ambiguous and the name lacks
commentary value.

If we take away __always_inline's for-performance role then what
remains?  __always_inline is for tricky things where the compiler needs
to be coerced into doing what we want?

IOW, I wonder if we should take your concept further, create more
fine-grained controls over this which have self-explanatory names.

mm/ alone has 74 __always_inlines, none are documented, I don't know
why they're present, many are probably wrong.

Shit, uninlining only __get_user_pages_locked does this:

   text	   data	    bss	    dec	    hex	filename
 115703	  14018	     64	 129785	  1faf9	mm/gup.o
 103866	  13058	     64	 116988	  1c8fc	mm/gup.o-after