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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 44D74C43603 for ; Fri, 20 Dec 2019 10:22:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 142E424683 for ; Fri, 20 Dec 2019 10:22:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576837345; bh=7kD4WZpoUBWtlhJGMRIhfgsM4IUYXBLNc4dysvjzAlc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=uODSF7a6EvrqEaWSUnMFqOvoIAtSZtSlwD962b7JAyNuEtIBWfIpu3BJFrMJBFRGq /OP7qUiYVkhjzYgk7s/xjZvU+o6gxZVxGbGJaJUs6RAiHFr3dw3XJee/LsYToevMlC U1st1fd9itcu2qoV0GH6ssT+6vdkOkBg3pM+54pI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727261AbfLTKWY (ORCPT ); Fri, 20 Dec 2019 05:22:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:54118 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727184AbfLTKWX (ORCPT ); Fri, 20 Dec 2019 05:22:23 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id ECF7624679; Fri, 20 Dec 2019 10:22:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576837341; bh=7kD4WZpoUBWtlhJGMRIhfgsM4IUYXBLNc4dysvjzAlc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=X6EMH0O7CJd/JUROxBWz5ymE3x/5G2Zi2sawHAsdgjHX35u+HPFo20A9EzVcW154W j6WndDIlMlBqBf7HVbPTgkEsosVBLfuYVqJG1Ctj0MYn6pSCLkp5m2Mz7WnOnzrHY0 DvfwazLMXiI+1Ab80EW3JE1m6zuV6K9962BlfgAw= Date: Fri, 20 Dec 2019 11:22:18 +0100 From: Greg Kroah-Hartman To: Marc Gonzalez Cc: Rafael Wysocki , LKML , Linux ARM , Robin Murphy , Dmitry Torokhov , Alexey Brodkin , Peter Zijlstra , Will Deacon , Russell King , Bjorn Andersson , Tejun Heo , Mark Brown Subject: Re: [RFC PATCH v1] devres: align devres.data strictly only for devm_kmalloc() Message-ID: <20191220102218.GA2259862@kroah.com> References: <74ae22cd-08c1-d846-3e1d-cbc38db87442@free.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 20, 2019 at 11:19:27AM +0100, Marc Gonzalez wrote: > On 17/12/2019 16:30, Marc Gonzalez wrote: > > > Commit a66d972465d15 ("devres: Align data[] to ARCH_KMALLOC_MINALIGN") > > increased the alignment of devres.data unconditionally. > > > > Some platforms have very strict alignment requirements for DMA-safe > > addresses, e.g. 128 bytes on arm64. There, struct devres amounts to: > > 3 pointers + pad_to_128 + data + pad_to_256 > > i.e. ~220 bytes of padding. > > > > Let's enforce the alignment only for devm_kmalloc(). > > > > Suggested-by: Robin Murphy > > Signed-off-by: Marc Gonzalez > > --- > > I had not been aware that dynamic allocation granularity on arm64 was > > 128 bytes. This means there's a lot of waste on small allocations. > > I suppose there's no easy solution, though. > > --- > > drivers/base/devres.c | 23 +++++++++++++---------- > > 1 file changed, 13 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/base/devres.c b/drivers/base/devres.c > > index 0bbb328bd17f..bf39188613d9 100644 > > --- a/drivers/base/devres.c > > +++ b/drivers/base/devres.c > > @@ -26,14 +26,7 @@ struct devres_node { > > > > struct devres { > > struct devres_node node; > > - /* > > - * Some archs want to perform DMA into kmalloc caches > > - * and need a guaranteed alignment larger than > > - * the alignment of a 64-bit integer. > > - * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same > > - * buffer alignment as if it was allocated by plain kmalloc(). > > - */ > > - u8 __aligned(ARCH_KMALLOC_MINALIGN) data[]; > > + u8 data[]; > > }; > > > > struct devres_group { > > @@ -789,9 +782,16 @@ static void devm_kmalloc_release(struct device *dev, void *res) > > /* noop */ > > } > > > > +#define DEVM_KMALLOC_PADDING_SIZE \ > > + (ARCH_KMALLOC_MINALIGN - sizeof(struct devres) % ARCH_KMALLOC_MINALIGN) > > + > > static int devm_kmalloc_match(struct device *dev, void *res, void *data) > > { > > - return res == data; > > + /* > > + * 'res' is dr->data (not DMA-safe) > > + * 'data' is the hand-aligned address from devm_kmalloc > > + */ > > + return res + DEVM_KMALLOC_PADDING_SIZE == data; > > } > > > > /** > > @@ -811,6 +811,9 @@ void * devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) > > { > > struct devres *dr; > > > > + /* Add enough padding to provide a DMA-safe address */ > > + size += DEVM_KMALLOC_PADDING_SIZE; > > + > > /* use raw alloc_dr for kmalloc caller tracing */ > > dr = alloc_dr(devm_kmalloc_release, size, gfp, dev_to_node(dev)); > > if (unlikely(!dr)) > > @@ -822,7 +825,7 @@ void * devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) > > */ > > set_node_dbginfo(&dr->node, "devm_kzalloc_release", size); > > devres_add(dev, dr->data); > > - return dr->data; > > + return dr->data + DEVM_KMALLOC_PADDING_SIZE; > > } > > EXPORT_SYMBOL_GPL(devm_kmalloc); > > Would anyone else have any suggestions, comments, insights, recommendations, > improvements, guidance, or wisdom? :-) > > I keep thinking about the memory waste caused by the strict alignment requirement > on arm64. Is there a way to inspect how much memory has been requested vs how much > has been allocated? (Turning on SLAB DEBUG perhaps?) > > Couldn't there be a kmalloc flag saying "this alloc will not require strict > alignment, so just give me something 8-byte aligned" ? Or you can not use the devm interface for lots of tiny allocations :) thanks, greg k-h