From: Hao Li <hao.li@linux.dev>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Vlastimil Babka <vbabka@kernel.org>, Harry Yoo <harry@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
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
Date: Tue, 3 Nov 2026 17:44:13 +0800 [thread overview]
Message-ID: <aumssHCOA4D_BFm1@fedora> (raw)
In-Reply-To: <20261102082730.12430-1-yangtiezhu@loongson.cn>
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.
Personally, I feel the commit message is a bit lengthy for a simple
comment-only patch. It might be better to keep it concise and just directly
state the purpose of the change.
--
Thanks,
Hao
prev parent reply other threads:[~2026-11-03 9:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-02 8:27 Tiezhu Yang
2026-11-02 14:49 ` Harry Yoo
2026-11-03 1:52 ` Tiezhu Yang
2026-11-03 9:44 ` Hao Li [this message]
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