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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5297CC54EAA for ; Fri, 27 Jan 2023 06:37:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=dmzGlhVDvFxbdiggt0kELKfUe374HwWz059ds2bUDm0=; b=aGyRMWs3awK0Th b8be+VskIVot0SQ9TlikmuIMKNo/a2tvN4eXaxGLS5Qx9gsUwflYu9QUoeRj/KH95obcY0jlLkJz5 ui6RicVoACL5W0KNtittzGQ1yS/aQqCrg8MFmHGJf2SU2IIrtmqsxSzEzQVX6XuDe33GAU6LFqr6g TgI+AjhZ4ndtV9/RrcR6mtSMLMDMmZtN5RM0rkzipZa8zAmVJi7RxpOdKVWmuNAtBXzdVGnGTGMDk aRvuQwny6SdST3/u2n45XGDwmHytauKV942tLaJ+Le4djIYqbDkkqmfvBCfpfk7LryJY0Ew3wUR5N mPuTTGiqMscz5DEpJNTA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pLILM-00DLgB-9o; Fri, 27 Jan 2023 06:36:12 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1pLILE-00DLes-Q1 for linux-arm-kernel@lists.infradead.org; Fri, 27 Jan 2023 06:36:09 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7A69F68D09; Fri, 27 Jan 2023 07:35:55 +0100 (CET) Date: Fri, 27 Jan 2023 07:35:55 +0100 From: Christoph Hellwig To: Dave Hansen Cc: Georgi Djakov , catalin.marinas@arm.com, will@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, hch@lst.de, m.szyprowski@samsung.com, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, djakov@kernel.org Subject: Re: [RFC] mm: Allow ZONE_DMA32 to be disabled via kernel command line Message-ID: <20230127063555.GA3300@lst.de> References: <20230126164352.17562-1-quic_c_gdjako@quicinc.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230126_223605_009904_1AF6AC04 X-CRM114-Status: GOOD ( 15.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Jan 26, 2023 at 10:51:17AM -0800, Dave Hansen wrote: > > Also, what are the practical implications here? There are obviously an > ever decreasing number of 32-bit DMA devices out there. Somebody that > has one and uses this option might be sad because now they're stuck > using ZONE_DMA which is quite tiny. > > What other ZONE_DMA32 users are left? Will anyone else care? There is > some DMA32 slab and vmalloc() functionality remaining. Is it impacted? DMA32 never supported lab. But < 64-bit DMA device are unfortunately still not uncommon, and configuring out ZONE_DMA32 breaks them pretty badly as we guarantee that a DMA mask of 32-bit always works. So I'm not only very much against this patch, but also the currently existing way to configure out ZONE_DMA32 on arm64, which needs to go away. If people want ZONE_DMA32 to go away we need something to replace it first, like a large enough CMA region in the 32-bit addressable range. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel