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Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Jason Xing , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Jiayuan Chen , Willem de Bruijn , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH v4 2/7] mm/slab: Give bucket caches the alignment of the caches they mirror Message-ID: <202609241759.28EC6970@keescook> References: <20260921075811.too.775-kees@kernel.org> <20260921075820.1718334-2-kees@kernel.org> <202609211620.342AAA61@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: CB3682000A X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 7w6wxzx5kbhg49cqokqtmwohbdks3fsh X-HE-Tag: 1790298041-131014 X-HE-Meta: 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 0LOOqOAb QRRz9Ml5pKtakh1jURLzscEuOO4q0XyxLJ+gEzg/eX8pLFU/+zxTPoCaGLNuilkC8skr1Rv2gW+GhW3c7fNQCGv0MHKhLcdgIPNlFFzU7A89Xy7aOV/D6SWEhhArl7t/+91PeolSRv321obdFf16Qktlw4c70gSvxRGmWTBOVj5qTl3dEs366U3eXrZl3A4D51N2HX34jBSslCdhOGkyp6MDV2VG6dO5wn74zuOt90HqLiqkASKMDWk0ihAjgr2hNyw17 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 24, 2026 at 07:22:58PM +0100, Harry Yoo wrote: > On Mon, Sep 21, 2026 at 04:25:25PM -0700, Kees Cook wrote: > > On Mon, Sep 21, 2026 at 02:17:21PM +0100, Harry Yoo wrote: > > > On Mon, Sep 21, 2026 at 12:58:13AM -0700, Kees Cook wrote: > > > > if (WARN_ON(!cache_name)) > > > > goto fail; > > > > (*b)[aligned_idx] = kmem_cache_create_usercopy(cache_name, size, > > > > - 0, flags, cache_useroffset, > > > > + kmalloc_caches[KMALLOC_NORMAL][idx]->align, > > > > + flags, cache_useroffset, > > > > cache_usersize, ctor); > > > > kfree(cache_name); > > > > if (WARN_ON(!(*b)[aligned_idx])) > > > > It looks "obviously correct", but I probably failed to correctly > > describe it. I'm happy to do whatever here. > > That is correct, but is there any reason why kmem_buckets users should > not specify their own alignment requirement and inherit the alignment > from kmalloc? > > For DMA yeah it might be confusing for every user to figure out that > the alignment should be __kmalloc_minalign(), but otherwise there isn't > really a good enough reason to inherit the alignment from kmalloc, no? Oh, so you mean explicitly add an alignment arg to kmem_buckets_create()? And perhaps if _that_ one is "0" we can fallback to whatever kmalloc_caches uses? -- Kees Cook