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

Suren Baghdasaryan
2026-01-21T17:39:14Z

On Tue, Jan 20, 2026 at 12:07 PM Hao Li <hao.li@linux.dev> wrote:
>
> 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>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

>
> --
> Thanks,
> Hao