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

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Message-ID: <CAJuCfpFTJUowSAjNum1zecDJYuyUi84vUNkoNNf=CnUwpsTVeg@mail.gmail.com>
Date: Tue, 13 Jan 2026 08:33:43 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: ranxiaokai627@....com, Liam.Howlett@...cle.com, akpm@...ux-foundation.org, 
	corbet@....net, david@...nel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, lorenzo.stoakes@...cle.com, 
	mhocko@...e.com, ran.xiaokai@....com.cn, rppt@...nel.org, vbabka@...e.cz
Subject: Re: [PATCH] alloc_tag: remove sysctl prefix from mem_profiling boot parameter

On Mon, Jan 12, 2026 at 7:50 PM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> On Tue, Jan 13, 2026 at 03:27:35AM +0000, ranxiaokai627@....com wrote:
> > >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?
> >
> > Actually no kernel bug or funtional defect was observed through testing.
> > Via code reading, i found after commit [1],
> > boot parameters prefixed with sysctl is processed redundantly.

I was able to reproduce the warning by enabling
CONFIG_MEM_ALLOC_PROFILING,
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
CONFIG_MEM_ALLOC_PROFILING_DEBUG, CONFIG_SYSCTL and setting
CONFIG_CMDLINE="1".
The fix I posted eliminates that warning. Ran, you can post my
suggestion yourself with me as Suggested-by or I can post it with you
as Reported-by. Let me know your preference.

>
> When bcachefs was in the kernel, I spent an inordinate amount of time in
> code reviews trying to convince people that yes, they really do need to
> be testing their code.
>
> Strangely enough, I have never had this issue with project contributors
> who did not come to the project by way of the kernel community... :)