From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06B1AC433FE for ; Sun, 17 Apr 2022 08:32:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233624AbiDQIdy (ORCPT ); Sun, 17 Apr 2022 04:33:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233628AbiDQIdx (ORCPT ); Sun, 17 Apr 2022 04:33:53 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2CAB020192 for ; Sun, 17 Apr 2022 01:31:18 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7393EB80AAD for ; Sun, 17 Apr 2022 08:31:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 03810C385A4; Sun, 17 Apr 2022 08:31:12 +0000 (UTC) Date: Sun, 17 Apr 2022 09:31:09 +0100 From: Catalin Marinas To: Herbert Xu Cc: Ard Biesheuvel , Will Deacon , Marc Zyngier , Arnd Bergmann , Greg Kroah-Hartman , Andrew Morton , Linus Torvalds , Linux Memory Management List , Linux ARM , Linux Kernel Mailing List , "David S. Miller" Subject: Re: [PATCH 07/10] crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 17, 2022 at 04:08:22PM +0800, Herbert Xu wrote: > On Fri, Apr 15, 2022 at 01:38:15PM +0200, Ard Biesheuvel wrote: > > If this is the case, things are already broken today. We never take > > ARCH_DMA_MINALIGN into account when adding the driver ctx size to the > > overall allocation size. > > No it's not broken because kmalloc guarantees alignment. For > example, if ARCH_DMA_MINALIGN is 128 bytes, then kmalloc will > always return a pointer that's 128-byte aligned. That guarantees > this object and the next object are on different cache-lines. > > If you reduce the kmalloc minimum alignment to 64 bytes, then > the two neighbouring objects can share cache-lines, even if > each object is bigger than 128 bytes (e.g., if they were 192 > bytes each). Not with my series, the non-sharing of cache lines is preserved. kmalloc() still returns objects aligned to a cache-line. ARCH_DMA_MINALIGN was chosen as the cover-all value for all SoCs supported but I want to reduce the kmalloc() alignment to a cache line size if a platform has a cache line smaller than ARCH_DMA_MINALIGN (most arm64 SoCs have a cache line of 64 bytes rather than 128). -- Catalin