Re: [PATCH v2] mm/slub: clamp slab_min_order to MAX_PAGE_ORDER

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 10/11/26 03:48, Sang-Heon Jeon wrote:
> setup_slub_max_order() clamps slab_max_order to MAX_PAGE_ORDER, but
> setup_slub_min_order() has no such clamp.
> 
> The buddy allocator cannot allocate more than 2^MAX_PAGE_ORDER pages
> at once, so slab_min_order above it makes no sense.
> 
> If slab_min_order is set above MAX_PAGE_ORDER, it can even panic at
> boot or invoke undefined behavior in order_objects().
> 
> So clamp slab_min_order to MAX_PAGE_ORDER as well.
> 
> Fixes: 81819f0fc828 ("SLUB core")
> Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>

Hi,

this is effectively part of my bigger refactor here:

https://lore.kernel.org/linux-mm/20260923-slub_tiny_rework-v1-1-a0e66d536eb5@kernel.org/

Thanks,
Vlastimil

> ---
> Changes from v1 [1]
> - Change fixes tag to 81819f0fc828 ("SLUB core")
> - Remove stable tag
> 
> [1] https://lore.kernel.org/all/20261007163403.1643768-1-ekffu200098@gmail.com/#t
> ---
>  mm/slub.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 1559cbace469..8400df7c222e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -8354,6 +8354,8 @@ static int __init setup_slub_min_order(const char *str, const struct kernel_para
>  	if (ret)
>  		return ret;
>  
> +	slub_min_order = min_t(unsigned int, slub_min_order, MAX_PAGE_ORDER);
> +
>  	if (slub_min_order > slub_max_order)
>  		slub_max_order = slub_min_order;
>  
> 
> base-commit: d755441b7672c74f29d1241ffdd2b067ecab1ca0