linux-kernel - Re: [PATCH] alloc_tag: remove sysctl prefix from mem

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Message-ID: <aWMLQkvushKidjQQ@moria.home.lan>
Date: Sat, 10 Jan 2026 21:33:54 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: ranxiaokai627@....com
Cc: surenb@...gle.com, vbabka@...e.cz, akpm@...ux-foundation.org, 
	david@...nel.org, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, 
	rppt@...nel.org, mhocko@...e.com, corbet@....net, linux-mm@...ck.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, ran.xiaokai@....com.cn
Subject: Re: [PATCH] alloc_tag: remove sysctl prefix from mem_profiling boot
 parameter

On Fri, Jan 09, 2026 at 06:24:19AM +0000, ranxiaokai627@....com wrote:
> From: Ran Xiaokai <ran.xiaokai@....com.cn>
> 
> Boot parameters prefixed with "sysctl." are processed separately
> during the final stage of system initialization via kernel_init()->
> do_sysctl_args(). Since mem_profiling support should be parsed
> in early boot stage, it is unsuitable for centralized handling
> in do_sysctl_args().
> Also, when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled,
> the sysctl.vm.mem_profiling entry is not writable and will cause
> a warning. To prevent duplicate processing of sysctl.vm.mem_profiling,
> rename the boot parameter to "mem_profiling".
> 
> Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>

How was this observed/detected?

My reading of early_param() would seem to indicate that
setup_early_mem_profiling() is getting called at the appropriate time -
and then additionally a second time by do_sysctl_args(), which then
becomes a noop.

So the only bug would seem to be that the sysctl is not writeable in
debug mode? There's an easier fix for that one...