From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Fri, 22 Mar 2013 19:33:16 +0000 Subject: [PATCH 5/5] arm: dts: Convert mvebu device tree files to 64 bits In-Reply-To: <20130322174300.GA10230@obsidianresearch.com> References: <1363883179-1361-1-git-send-email-gregory.clement@free-electrons.com> <20130322062854.GS21478@lunn.ch> <20130322174300.GA10230@obsidianresearch.com> Message-ID: <201303221933.16426.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Friday 22 March 2013, Jason Gunthorpe wrote: > At a certain point low mem exhaustion becomes a serious issue for > Linux, a system that can't DMA to 85% of its memory is incredibly > broken, IMHO. A lot of workloads will also suffer from lowmem exhaustion even without the DMA zone problem. If course the combination is particularly nasty because now the kernel has a to kmap() a user page in order to copy the dma data in and out of lowmem. I'm sure there are even workloads that perform well with more than 16GB, but I can't think of any right now. I would expect that 4 or 8 GB is where it gets quite silly for most workloads, but troubles start as soon as you go beyond 1GB. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 5/5] arm: dts: Convert mvebu device tree files to 64 bits Date: Fri, 22 Mar 2013 19:33:16 +0000 Message-ID: <201303221933.16426.arnd@arndb.de> References: <1363883179-1361-1-git-send-email-gregory.clement@free-electrons.com> <20130322062854.GS21478@lunn.ch> <20130322174300.GA10230@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130322174300.GA10230-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: "devicetree-discuss" To: Jason Gunthorpe Cc: Lior Amsalem , Andrew Lunn , Ike Pan , Nadav Haklai , David Marlin , Yehuda Yitschak , Tawfik Bayouk , Dan Frazier , Eran Ben-Avi , Leif Lindholm , Sebastian Hesselbarth , Jason Cooper , Jon Masters , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Rob Herring , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Chris Van Hoof , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Maen Suleiman , Shadi Ammouri List-Id: devicetree@vger.kernel.org On Friday 22 March 2013, Jason Gunthorpe wrote: > At a certain point low mem exhaustion becomes a serious issue for > Linux, a system that can't DMA to 85% of its memory is incredibly > broken, IMHO. A lot of workloads will also suffer from lowmem exhaustion even without the DMA zone problem. If course the combination is particularly nasty because now the kernel has a to kmap() a user page in order to copy the dma data in and out of lowmem. I'm sure there are even workloads that perform well with more than 16GB, but I can't think of any right now. I would expect that 4 or 8 GB is where it gets quite silly for most workloads, but troubles start as soon as you go beyond 1GB. Arnd