From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 26 Aug 1999 18:27:51 +0200 (CEST) From: Andrea Arcangeli Subject: Re: [bigmem-patch] 4GB with Linux on IA32 In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Alan Cox Cc: Linus Torvalds , kanoj@google.engr.sgi.com, sct@redhat.com, Gerhard.Wichert@pdb.siemens.de, Winfried.Gerhard@pdb.siemens.de, linux-kernel@vger.rutgers.edu, linux-mm@kvack.org, linux-usb@suse.com List-ID: On Tue, 17 Aug 1999, Alan Cox wrote: >of bus addressses of vmalloc pages. I don't think the 4Gig patch breaks it >at all. In the ideal world virt_to_bus() would work on vmalloc pages. It Yes, the bigmem patch doesn't break bttv. bttv alloc the DMA-pool via vmalloc and with the bigmem patch applyed vmalloc prefere the bigmem pages so the DMA-pool will be always alloced in bigmem memory. But using vmalloc all bigmem pages will have a valid virt-to-phys translation. (Only GFP may return a pointer without a valid virt-to-phys translation if __GFP_BIGMEM is been specifyed in the gfp_mask.) So the kernel can also copy-from/to-user the DMA pool using the vmalloc addresses since it's a _valid_ address. Via mmap the vmalloced pages will be remapped to userspace memory and that's fine as well. Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/