From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 644D26B0089 for ; Thu, 23 Dec 2010 09:08:27 -0500 (EST) MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: text/plain; charset=ISO-8859-1 Received: from spt2.w1.samsung.com ([210.118.77.13]) by mailout3.w1.samsung.com (Sun Java(tm) System Messaging Server 6.3-8.04 (built Jul 29 2009; 32bit)) with ESMTP id <0LDV00AAMWM0BF60@mailout3.w1.samsung.com> for linux-mm@kvack.org; Thu, 23 Dec 2010 14:08:24 +0000 (GMT) Received: from linux.samsung.com ([106.116.38.10]) by spt2.w1.samsung.com (iPlanet Messaging Server 5.2 Patch 2 (built Jul 14 2004)) with ESMTPA id <0LDV00B2FWLXCY@spt2.w1.samsung.com> for linux-mm@kvack.org; Thu, 23 Dec 2010 14:08:22 +0000 (GMT) Date: Thu, 23 Dec 2010 15:08:21 +0100 From: Tomasz Fujak Subject: Re: [PATCHv8 00/12] Contiguous Memory Allocator In-reply-to: <20101223135120.GL3636@n2100.arm.linux.org.uk> Message-id: <4D1357D5.9000507@samsung.com> References: <20101223100642.GD3636@n2100.arm.linux.org.uk> <87k4j0ehdl.fsf@erwin.mina86.com> <20101223135120.GL3636@n2100.arm.linux.org.uk> Sender: owner-linux-mm@kvack.org To: Russell King - ARM Linux Cc: Michal Nazarewicz , Kyungmin Park , linux-arm-kernel@lists.infradead.org, Daniel Walker , Johan MOSSBERG , Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ankita Garg , Andrew Morton , linux-media@vger.kernel.org, KAMEZAWA Hiroyuki , Marek Szyprowski List-ID: On 2010-12-23 14:51, Russell King - ARM Linux wrote: > On Thu, Dec 23, 2010 at 02:41:26PM +0100, Michal Nazarewicz wrote: >> Russell King - ARM Linux writes: >>> Has anyone addressed my issue with it that this is wide-open for >>> abuse by allocating large chunks of memory, and then remapping >>> them in some way with different attributes, thereby violating the >>> ARM architecture specification? >>> >>> In other words, do we _actually_ have a use for this which doesn't >>> involve doing something like allocating 32MB of memory from it, >>> remapping it so that it's DMA coherent, and then performing DMA >>> on the resulting buffer? >> Huge pages. >> >> Also, don't treat it as coherent memory and just flush/clear/invalidate >> cache before and after each DMA transaction. I never understood what's >> wrong with that approach. > If you've ever used an ARM system with a VIVT cache, you'll know what's > wrong with this approach. > > ARM systems with VIVT caches have extremely poor task switching > performance because they flush the entire data cache at every task switch > - to the extent that it makes system performance drop dramatically when > they become loaded. > > Doing that for every DMA operation will kill the advantage we've gained > from having VIPT caches and ASIDs stone dead. This statement effectively means: don't map dma-able memory to the CPU unless it's uncached. Have I missed anything? > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org