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 l/aZQEjb 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > --- What a nice cleanup! Looks good to me, Reviewed-by: Harry Yoo with a nit below. > mm/slab.h | 1 - > mm/slub.c | 144 +++++++++++++------------------------------------------------- > 2 files changed, 29 insertions(+), 116 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 4efec41b6445..e9a0738133ed 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -5268,10 +5196,11 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node) > if (!(s->flags & __CMPXCHG_DOUBLE) && !kmem_cache_debug(s)) > /* > * kmalloc_nolock() is not supported on architectures that > - * don't implement cmpxchg16b, but debug caches don't use > - * per-cpu slab and per-cpu partial slabs. They rely on > - * kmem_cache_node->list_lock, so kmalloc_nolock() can > - * attempt to allocate from debug caches by > + * don't implement cmpxchg16b and thus need slab_lock() > + * which could be preempted by a nmi. nit: I think now this limitation can be removed because the only slab lock used in the allocation path is get_partial_node() -> __slab_update_freelist(), but it is always used under n->list_lock. Being preempted by a NMI while holding the slab lock is fine because NMI context should fail to acquire n->list_lock and bail out. But no hurry on this, it's probably not important enough to delay this series :) > + * But debug caches don't use that and only rely on > + * kmem_cache_node->list_lock, so kmalloc_nolock() can attempt > + * to allocate from debug caches by > * spin_trylock_irqsave(&n->list_lock, ...) > */ > return NULL; > -- Cheers, Harry / Hyeonggon