Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 6 Jul 2001 05:00:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 6 Jul 2001 05:00:08 -0400 Received: from hermine.idb.hist.no ([158.38.50.15]:58635 "HELO hermine.idb.hist.no") by vger.kernel.org with SMTP id ; Fri, 6 Jul 2001 04:59:56 -0400 Message-ID: <3B457DE6.AFEE6696@idb.hist.no> Date: Fri, 06 Jul 2001 10:59:18 +0200 From: Helge Hafting X-Mailer: Mozilla 4.76 [en] (X11; U; Linux 2.4.6 i686) X-Accept-Language: no, en MIME-Version: 1.0 To: Vasu Varma P V CC: linux-kernel@vger.kernel.org Subject: Re: DMA memory limitation? In-Reply-To: <3B4453E6.F4342781@techmas.hcltech.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Vasu Varma P V wrote: > > Hi, > > Is there any limitation on DMA memory we can allocate using > kmalloc(size, GFP_DMA)? I am not able to acquire more than > 14MB of the mem using this on my PCI SMP box with 256MB ram. > I think there is restriction on ISA boards of 16MB. > Can we increase it ? You can allocate a lot more memory for your pci activities. No problem there. Just drop the "GFP_DMA" and you'll get up to 1G or so. You shouldn't use GFP_DMA because PCI cards don't need that. Only ISA cards needs GFP_DMA because they can't use more than 16M. So obviously GFP_DMA is limited to 16M because it is really ISA_DMA. PCI don't need such special tricks, so don't use GFP_DMA! Your PCI cards is able to DMA into any memory, including the non-GFP_DMA memory. > but we have a macro in include/asm-i386/dma.h, > MAX_DMA_ADDRESS (PAGE_OFFSET+0x1000000). > > if i change it to a higher value, i am able to get more dma > memory. Is there any way i can change this without compiling > the kernel? > No matter what you do, DON'T change that. Yeah, you'll get a bigger GFP_DMA pool, but that'll break each and every ISA card that tries to allocate GFP_DMA memory. You achieve exactly the same effect for your PCI card by ditching the GFP_DMA parameter, but then you achieve it without breaking ISA cards. Helge Hafting - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/