Re: [PATCH v3 14/21] slab: simplify kmalloc_nolock()

[Hao Li]

On Fri, Jan 16, 2026 at 03:40:34PM +0100, Vlastimil Babka wrote:
> The kmalloc_nolock() implementation has several complications and
> restrictions due to SLUB's cpu slab locking, lockless fastpath and
> PREEMPT_RT differences. With cpu slab usage removed, we can simplify
> things:
> 
> - relax the PREEMPT_RT context checks as they were before commit
>   a4ae75d1b6a2 ("slab: fix kmalloc_nolock() context check for
>   PREEMPT_RT") and also reference the explanation comment in the page
>   allocator
> 
> - the local_lock_cpu_slab() macros became unused, remove them
> 
> - we no longer need to set up lockdep classes on PREEMPT_RT
> 
> - we no longer need to annotate ___slab_alloc as NOKPROBE_SYMBOL
>   since there's no lockless cpu freelist manipulation anymore
> 
> - __slab_alloc_node() can be called from kmalloc_nolock_noprof()
>   unconditionally. It can also no longer return EBUSY. But trylock
>   failures can still happen so retry with the larger bucket if the
>   allocation fails for any reason.
> 
> Note that we still need __CMPXCHG_DOUBLE, because while it was removed
> we don't use cmpxchg16b on cpu freelist anymore, we still use it on
> slab freelist, and the alternative is slab_lock() which can be
> interrupted by a nmi. Clarify the comment to mention it specifically.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  mm/slab.h |   1 -
>  mm/slub.c | 144 +++++++++++++-------------------------------------------------
>  2 files changed, 29 insertions(+), 116 deletions(-)
> 

Looks good to me.
Reviewed-by: Hao Li <hao.li@xxxxxxxxx>

-- 
Thanks,
Hao