linux-kernel - Re: [PATCH] mm/slub: fix help comment of SLUB_DEBUG[

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Message-ID: <ZBAUrPq+Ic/VSzF5@vernon-pc>
Date:   Tue, 14 Mar 2023 14:33:34 +0800
From:   Vernon Yang <vernon2gm@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slub: fix help comment of SLUB_DEBUG[_ON]

On Mon, Mar 13, 2023 at 05:26:19PM +0100, Vlastimil Babka wrote:
> On 2/23/23 02:03, Hyeonggon Yoo wrote:
> > On Thu, Feb 23, 2023 at 07:20:58AM +0800, Vernon Yang wrote:
> >> Since commit 081248de0a02 ("kset: move /sys/slab to /sys/kernel/slab"),
> >> the SYSFS path of slab was modified, so fix up the help comment of
> >> SLUB_DEBUG to use the correct one.
> >>
> >> And now the "slub_debug" parameter on boot that is support for more
> >> fine grained debug control, so fix up help comment of SLUB_DEBUG_ON
> >> for "no support" to "support".
> >>
> >> Signed-off-by: Vernon Yang <vernon2gm@...il.com>
> >> ---
> >>  mm/Kconfig.debug | 12 ++++++------
> >>  1 file changed, 6 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
> >> index fca699ad1fb0..732043bf56c6 100644
> >> --- a/mm/Kconfig.debug
> >> +++ b/mm/Kconfig.debug
> >> @@ -61,8 +61,8 @@ config SLUB_DEBUG
> >>  	help
> >>  	  SLUB has extensive debug support features. Disabling these can
> >>  	  result in significant savings in code size. This also disables
> >> -	  SLUB sysfs support. /sys/slab will not exist and there will be
> >> -	  no support for cache validation etc.
> >> +	  SLUB sysfs support. /sys/kernel/slab will not exist and there
> >> +	  will be no support for cache validation etc.
> >
> > After commit ab4d5ed5eeda ("slub: Enable sysfs support for !CONFIG_SLUB_DEBUG"),
> > "Disabling SLUB_DEBUG also disables SLUB sysfs support" is not true anymore.

Yes, You are right. Thanks.

>
> Yeah we could say that /sys/kernel/slab will exist but will not provide e.g.
> cache validation.

OK.

>
> >>  config SLUB_DEBUG_ON
> >>  	bool "SLUB debugging on by default"
> >> @@ -73,10 +73,10 @@ config SLUB_DEBUG_ON
> >>  	  Boot with debugging on by default. SLUB boots by default with
> >>  	  the runtime debug capabilities switched off. Enabling this is
> >>  	  equivalent to specifying the "slub_debug" parameter on boot.
> >> -	  There is no support for more fine grained debug control like
> >> -	  possible with slub_debug=xxx. SLUB debugging may be switched
> >> -	  off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
> >> -	  "slub_debug=-".
> >> +	  There is support for more fine grained debug control like
> >> +	  possible with slub_debug=xxx, details in Documentation/mm/slub.rst.
> >> +	  SLUB debugging may be switched off in a kernel built with
> >> +	  CONFIG_SLUB_DEBUG_ON by specifying "slub_debug=-".
> >
> > I think this is a misunderstanding. SLUB_DEBUG_ON is equivalent to

Yeah, This is a misunderstanding. I remove this.

> > passing boot parameter slub_debug=FUPZ, and what the help text says is that
> >
> > "You can enable slub debugging by default using this config option but
> >  there is no support for fine-grained control like what slub_debug
> >  boot parameter provides."
> >
> >  IOW SLUB_DEBUG_ON cannot be used to have same effect as passing
> >  something like slub_debug=F.
>
> Agree with both comments. Vernon, will you send an updated patch?

Ok, I'll be sending a new patch shortly.

>
> >>
> >>  config PAGE_OWNER
> >>  	bool "Track page owner"
> >> --
> >> 2.34.1
> >>
> >>
>