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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 9C015C433E0 for ; Mon, 8 Jun 2020 12:04:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 738882078C for ; Mon, 8 Jun 2020 12:04:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729743AbgFHMEB (ORCPT ); Mon, 8 Jun 2020 08:04:01 -0400 Received: from foss.arm.com ([217.140.110.172]:51946 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729665AbgFHMEB (ORCPT ); Mon, 8 Jun 2020 08:04:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9697B1FB; Mon, 8 Jun 2020 05:04:00 -0700 (PDT) Received: from [10.57.9.113] (unknown [10.57.9.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 84C973F52E; Mon, 8 Jun 2020 05:03:59 -0700 (PDT) Subject: Re: [PATCH] dma-pool: Fix too large DMA pools on medium systems To: Geert Uytterhoeven , Christoph Hellwig , Marek Szyprowski , David Rientjes Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20200608085231.8924-1-geert@linux-m68k.org> From: Robin Murphy Message-ID: <92b53a24-2f1f-2add-6bea-eeda7317520f@arm.com> Date: Mon, 8 Jun 2020 13:03:54 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200608085231.8924-1-geert@linux-m68k.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-06-08 09:52, Geert Uytterhoeven wrote: > On systems with at least 32 MiB, but less than 32 GiB of RAM, the DMA > memory pools are much larger than intended (e.g. 2 MiB instead of 128 > KiB on a 256 MiB system). > > Fix this by correcting the calculation of the number of GiBs of RAM in > the system. > > Fixes: 1d659236fb43c4d2 ("dma-pool: scale the default DMA coherent pool size with memory capacity") > Signed-off-by: Geert Uytterhoeven > --- > kernel/dma/pool.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c > index 35bb51c31fff370f..1c7eab2cc0498003 100644 > --- a/kernel/dma/pool.c > +++ b/kernel/dma/pool.c > @@ -175,8 +175,8 @@ static int __init dma_atomic_pool_init(void) > * sizes to 128KB per 1GB of memory, min 128KB, max MAX_ORDER-1. > */ > if (!atomic_pool_size) { > - atomic_pool_size = max(totalram_pages() >> PAGE_SHIFT, 1UL) * > - SZ_128K; > + unsigned long gigs = totalram_pages() >> (30 - PAGE_SHIFT); > + atomic_pool_size = max(gigs, 1UL) * SZ_128K; > atomic_pool_size = min_t(size_t, atomic_pool_size, > 1 << (PAGE_SHIFT + MAX_ORDER-1)); > } Nit: although this probably is right, it seems even less readable than the broken version (where at least some at-a-glance 'dimensional analysis' flags up "(number of pages) >> PAGE_SHIFT" as rather suspicious). How about a something a little more self-explanatory, e.g.: unsigned long pages = totalram_pages() * SZ_128K / SZ_1GB; atomic_pool_size = min(pages, MAX_ORDER_NR_PAGES) << PAGE_SHIFT; atomic_pool_size = max_t(size_t, atomic_pool_size, SZ_128K); ? Robin.