Re: [PATCH RFC v2 13/20] slab: simplify kmalloc_nolock()

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Jan 12, 2026 at 7:17 AM Vlastimil Babka <vbabka@suse.cz> 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:
>
> - 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>

sheaves and corresponding simplification of nolock() logic
in patches 11,12,13 look very promising to me.

Acked-by: Alexei Starovoitov <ast@kernel.org>