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Fri, 27 Mar 2026 03:25:12 -0700 (PDT) MIME-Version: 1.0 References: <20260327055846.248829-1-mikhail.v.gavrilov@gmail.com> In-Reply-To: From: Mikhail Gavrilov Date: Fri, 27 Mar 2026 15:25:00 +0500 X-Gm-Features: AQROBzB0-C_A6yb1j1_yQpuE6IZJqUuOjkwiTCpaemv5WY_Vd0aH5YH0GiQl35k Message-ID: Subject: Re: [PATCH] mm/slab: align kmalloc to cacheline when DMA API debugging is active To: "Harry Yoo (Oracle)" Cc: vbabka@kernel.org, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, stern@rowland.harvard.edu, linux@roeck-us.net, andy.shevchenko@gmail.com, hch@lst.de, Jeff.kirsher@gmail.com, Catalin Marinas Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: BF2F51C0013 X-Stat-Signature: akwhqswkcznz3hthsah636e5scmj9yt5 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774607113-492825 X-HE-Meta: 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 lv7Dgks4 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 27, 2026 at 1:43=E2=80=AFPM Harry Yoo (Oracle) wrote: > > Probably what I said was misleading... > > I didn't mean "the architecture is fine with overlapping cacheline". > > I meant "not defining ARCH_DMA_MINALIGN or defining it as smaller than > L1_CACHE_BYTES is how architectures tell kmalloc subsystem that > kmalloc objects don't have to be aligned with cacheline size." > Hi Harry, You're right, I was wrong about dma_get_cache_alignment() -- on x86_64 without ARCH_HAS_DMA_MINALIGN it returns 1, not L1_CACHE_BYTES. Sorry for the confusion. So your suggestion to suppress the warning in dma-debug when dma_get_cache_alignment() < L1_CACHE_BYTES would indeed work on x86_64 and other coherent platforms. I don't have a strong preference either way. Both approaches solve the problem: - slab side: prevents the overlap from happening - dma-debug side: tolerates the overlap when the arch says cacheline alignment isn't required for DMA Would you prefer I send a v2 with the dma-debug approach instead? Happy to go whichever direction the maintainers prefer. --=20 Best Regards, Mike Gavrilov.