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b=VovVNp2p/+WUkh+42qpFU37+vJQ1cl+UoTmYTPm1xl7saMJI+Sr6zkDbOCrK4LeN7 3tb4Ee551fvubrjMQuUNXkfN8dTq/3+M9DRYdH0ws/q3QUATZQPuXE/731HV4w1Tv2 GJZRoccrQPP3c+OzSPa/85YEs8QgAaBoRpK03ACzy4f4XrRIUjTC384+TkVpjZfmHd akciCQCD6Jdhsqj8YYEOseVq5zGkTZVsbwAeNT7gJ3orZStw6qef+FwCbKeiokrUS4 IWR1/46X8tRUE5yw2ZhcwAxKviT7O1hbKQJC6To6CIW1Twq9gtmkKXGck9WA6QAheH f+UJyNEqZ48SQ== Date: Mon, 2 Nov 2026 14:49:40 +0000 From: Harry Yoo To: Tiezhu Yang Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, loongarch@lists.linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm/slub: Genericize x86-specific cmpxchg16b comment Message-ID: References: <20261102082730.12430-1-yangtiezhu@loongson.cn> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261102082730.12430-1-yangtiezhu@loongson.cn> X-Rspamd-Queue-Id: F387B140010 X-Stat-Signature: nqao1assow5fsfq4bdjyca81juoys9rd X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793630983-501091 X-HE-Meta: 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 sM13lucc hs3It2tAsl0fbUrRHTP6Ik1QPEZRfjMJZlqYVAdTXa9X5KZxj2wIaH7fFBQmowFqKAvGD4700Z34oQhjZCyMzpKmalZBrKBl/ICfkjcZT51GBVcCc5njRCj5QoKzH0rA6TlUNTZBoJuClLWUOdhbi90oGQdXSUG3m8fEvY9yVZEnCP+2uxf7c+3bJdJSCnCsYSq/4J/JXRgdXj1KbOYb/aHor0/T1XoO/CPlzlgICAx2lpD2PxfLDphybPdL+jfCS97V1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Nov 02, 2026 at 04:27:30PM +0800, Tiezhu Yang wrote: > The kmalloc_nolock() infrastructure relies on slab caches with double-word > atomic cmpxchg capabilities (__CMPXCHG_DOUBLE). The current inline comment > in __kmalloc_nolock_noprof() uses 'cmpxchg16b' as the prerequisite hardware > capability. > > However, "cmpxchg16b" is an x86-specific instruction mnemonic (CX16). On > modern architectures supported by the Linux kernel, this 128-bit atomic > primitive is satisfied by different hardware implementations: > - arm64: satisfies it via LSE atomics ('casp' instruction) > - s390: satisfies it via native 'cdsg' instruction > - riscv: satisfies it via ZACAS extension ('amocas.q' instruction) > - loongarch: satisfies it via SCQ extension (using an 'll.d'/'sc.q' loop) > > Update the comment to refer to "128-bit atomic cmpxchg" to accurately > describe the cross-platform hardware invariant needed by the lockless > allocator, and to avoid misleading developers of non-x86 archs. > > Signed-off-by: Tiezhu Yang > --- > mm/slub.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 45e077c7526c..216bc6b5d776 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5589,8 +5589,8 @@ static void *__kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_f > if (!(s->flags & __CMPXCHG_DOUBLE) && !kmem_cache_debug(s)) > /* > * kmalloc_nolock() is not supported on architectures that > - * don't implement cmpxchg16b and thus need slab_lock() > - * which could be preempted by a nmi. > + * don't implement 128-bit atomic cmpxchg and thus need > + * slab_lock() which could be preempted by a nmi. maybe "double-width atomic cmpxchg" is more accurate considering e.g.) x86-32 implements cmpxchg8b? > * 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 > -- > 2.42.0 > -- Cheers, Harry / Hyeonggon