From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <45790212.8000608@goop.org> Date: Thu, 07 Dec 2006 22:11:30 -0800 From: Jeremy Fitzhardinge MIME-Version: 1.0 Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated References: <20061204113051.4e90b249.akpm@osdl.org> <20061204120611.4306024e.akpm@osdl.org> <20061204131959.bdeeee41.akpm@osdl.org> <20061204142259.3cdda664.akpm@osdl.org> <20061205112541.2a4b7414.akpm@osdl.org> <20061205214721.GE20614@skynet.ie> <4578BE37.1010109@goop.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Mel Gorman , Andrew Morton , Linux Memory Management List , Linux Kernel Mailing List List-ID: Christoph Lameter wrote: > The same can be done using the virtual->physical mappings that exist on > many platforms for the kernel address space (ia64 dynamically calculates > those, x86_64 uses a page table with 2M pages for mapping the kernel). Yes, that's basically what Xen does - there's a nonlinear mapping from kernel virtual to machine pages (and usermode pages are put through the same transformation before being mapped). > The > problem is that the 1-1 mapping between physical and virtual addresses > will have to be (at least partially) sacrificed which may lead to > complications with DMA devices. > Yes, any driver which expects contigious kernel pages to be physically contigious will be sorely disappointed. This isn't too hard to deal with (since such drivers are often buggy anyway, making poor assumptions about the relationship between physical addresses and bus addresses). An IOMMU could help as well. J -- 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/ . Don't email: email@kvack.org