Re: [PATCH RFC 0/8] replace CONFIG_SLUB_TINY with a slab_tiny boot parameter

[Vlastimil Babka (SUSE)]

On 9/24/26 17:18, Harry Yoo wrote:
> On Wed, Sep 23, 2026 at 05:45:05PM +0200, Vlastimil Babka (SUSE) wrote:
>> To sum up, after this series:
>> 
>> - CONFIG_SLUB_TINY is a deprecated option that has no interaction with
>>   other options and only controls the default behavior.
>> 
>> - New slab_tiny boot parameter controls the functionality (and can
>>   override CONFIG_SLUB_TINY in both directions).
>>
>> - slab_debug=N can effectively achieve most of slab_tiny and on a
>>   per-cache basic
> 
> Allowing "slab_tiny=0" doesn't make much sense given that
> CONFIG_SLUB_TINY is deprecated anyway. I was assuming specifying
> "slab_tiny" would enable it and not specifying it would disable it
> unless CONFIG_SLUB_TINY is set.

I was anticipating a possible autodetection in the future - i.e. "is this
system so tiny we should do it?" and a way to override to =0 may be useful.

> Also it's bit confusing to have multiple ways to achieve the same thing.
> Is there a reason why we can't interpret "slab_debug=N" as
> "slab_tiny_enabled = 1" internally and drop "slab_tiny" boot parameter?

"slab_debug=N" is a weird parameter to control the whole slab_tiny (which
does more than the slab_debug part). In my view it exists as a side-effect
to how slab_tiny is implemented. But because slab_tiny is implemented using
that, I thought it might make sense to expose slab_debug=N separately too.
It might be even useful in some debug scenario.

Whoever wants to use slab_tiny doesn't even need to know about slab_debug.

>> - the implementation is simpler with many ifdefs removed
>> 
>> [1] https://lore.kernel.org/all/CAHk-=wh-k04MsoEC0SGKff2Snm6bBF_e+0pHOKwaWv4umZ_SnQ@xxxxxxxxxxxxxx/
>> 
>> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>
>> ---
>> Vlastimil Babka (SUSE) (8):
>>       mm, slab: refactor slab_min/max_order handling
>>       mm, slab: introduce slab_debug=N
>>       mm, slab: rework KMALLOC_RECLAIM handling of SLUB_TINY
>>       mm, slab: make SLUB_TINY handling dynamic for sizing decisions
>>       mm, slab: convert CONFIG_SLUB_TINY checks to kmem_cache_debug()
>>       mm, slab: remove remaining compile-time checks for CONFIG_SLUB_TINY
>>       mm, slab: add slab_tiny boot param
>>       mm, slab: deprecate CONFIG_SLUB_TINY and reduce its Kconfig effects
>> 
>>  Documentation/admin-guide/kernel-parameters.txt |   4 +
>>  Documentation/admin-guide/mm/slab.rst           |  18 ++-
>>  include/linux/slab.h                            |  17 +--
>>  lib/Kconfig.kasan                               |   2 +-
>>  mm/Kconfig                                      |  16 ++-
>>  mm/Kconfig.debug                                |   2 +-
>>  mm/slab.h                                       |  32 +++--
>>  mm/slab_common.c                                |  12 +-
>>  mm/slub.c                                       | 149 +++++++++++-------------
>>  9 files changed, 120 insertions(+), 132 deletions(-)
>> ---
>> base-commit: b4218126d498275444f315b0ed4cef6add6beabc
>> change-id: 20260911-slub_tiny_rework-8f2634dd17a7
>> 
>