From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.11] helo=sc8-sf-mx1.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1CsqXD-0002XM-5b for user-mode-linux-devel@lists.sourceforge.net; Sun, 23 Jan 2005 14:48:43 -0800 Received: from pool-151-203-197-142.bos.east.verizon.net ([151.203.197.142] helo=ccure.user-mode-linux.org) by sc8-sf-mx1.sourceforge.net with esmtp (TLSv1:DES-CBC3-SHA:168) (Exim 4.41) id 1CsqXA-00045B-Ba for user-mode-linux-devel@lists.sourceforge.net; Sun, 23 Jan 2005 14:48:43 -0800 Message-Id: <200501240111.j0O1BtoI004687@ccure.user-mode-linux.org> Subject: Re: [uml-devel] memory In-Reply-To: Your message of "Sun, 23 Jan 2005 12:16:34 +0530." <267988DEACEC5A4D86D5FCD780313FBB03B12C4B@exch-03.noida.hcltech.com> References: <267988DEACEC5A4D86D5FCD780313FBB03B12C4B@exch-03.noida.hcltech.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii From: Jeff Dike Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Sun, 23 Jan 2005 20:11:55 -0500 To: "Vaibhav Sharma, Noida" Cc: user-mode-linux-devel@lists.sourceforge.net, Rob Landley , Doug Dumitru Vaibhavs@noida.hcltech.com said: > I have to build a simulator, to check the scalability limits in memory > management of linux. For this, the simulator will provide a large > amount of RAM (in GBs), even if the amout of physical memory is only > 512MB. > > Can UML be used for this purpose? I had seen the "mem" option in the > kernel switches option of UML. Can UML simulate such a case? Yes, it should be fine for what you want. > If it > does, how UML handles this? Specifically, can the UML kernel allocate > all this amount of memory It'll allocate a temp file of the appropriate size. If it's larger than what it can use for physical memory, the rest will be allocated as highmem. If you leave 2-level pagetables on, then you're limited to 4G. If you turn on 3-level pagetables, then you get up to 128G. doug@easyco.com said: > UML runs the client using a single user mode memory block as the > entire client's core. Thus the clients core size is limited to what > a single task can allocate as plain memory. No, it only maps the physical memory as a block. The highmem part is mapped on demand, as with i386. rob@landley.net said: > You could run out of virtual address space, though. Trying to map > more than a few gigabytes on a 32 bit machine is unlikely to work. With highmem, it's not all mapped at once. rob@landley.net said: > Not unless it's unmapping and remapping multiple mmaps. It is. > (There's > large file support, but trying to mmap a 5 gig chunk out of a large > file can't work: It does it a page at a time. > what would that mean? How could you generate an > offset into the last meg? The LFS interfaces take 64-bit offsets. > What would the pointer _be_?) What pointer? > The parent kernel's highmem support still doesn't provide more than 4 > gigabytes per application, and the UML kernel is one application. The host kernel's highmem support is totally irrelevant. There doesn't even need to be highmem support on the host. Jeff ------------------------------------------------------- This SF.Net email is sponsored by: IntelliVIEW -- Interactive Reporting Tool for open source databases. Create drag-&-drop reports. Save time by over 75%! Publish reports on the web. Export to DOC, XLS, RTF, etc. Download a FREE copy at http://www.intelliview.com/go/osdn_nl _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel