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

Hao Li
2026-01-20T12:07:02Z

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@suse.cz>
> ---
> 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@linux.dev>

--
Thanks,
Hao