Re: [PATCH] mm/slub: fix help comment of SLUB_DEBUG[_ON]

Vlastimil Babka
2023-03-13T16:26:24Z

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@gmail.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.

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

>> 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
> 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?

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