On Mon, 29 Jan 2007 13:54:38 -0800 (PST) Christoph Lameter <[EMAIL PROTECTED]> wrote:
> On Fri, 26 Jan 2007, Andrew Morton wrote: > > > > The main benefit is a significant simplification of the VM, leading to > > > robust and reliable operations and a reduction of the maintenance > > > headaches coming with the additional zones. > > > > > > If we would introduce the ability of allocating from a range of > > > physical addresses then the need for DMA zones would go away allowing > > > flexibility for device driver DMA allocations and at the same time we get > > > rid of special casing in the VM. > > > > None of this is valid. The great majority of machines out there will > > continue to have the same number of zones. Nothing changes. > > All 64 bit machine will only have a single zone if we have such a range > alloc mechanism. The 32bit ones with HIGHMEM wont be able to avoid it, > true. But all arches that do not need gymnastics to access their memory > will be able run with a single zone. What is "such a range alloc mechanism"? > > That's all a real cost, so we need to see *good* benefits to outweigh that > > cost. Thus far I don't think we've seen that. > > The real savings is the simplicity of VM design, robustness and > efficiency. We loose on all these fronts if we keep or add useless zones. > > The main reason for the recent problems with dirty handling seem to be due > to exactly such a multizone balancing issues involving ZONE_NORMAL and > HIGHMEM. Those problems cannot occur on single ZONE arches (this means > right now on a series of embedded arches, UML and IA64). > > Multiple ZONES are a recipie for VM fragility and result in complexity > that is difficult to manage. Why do I have to keep repeating myself? 90% of known FC6-running machines are x86-32. 90% of vendor-shipped kernels need all three zones. And the remaining 10% ship with multiple nodes as well. So please stop telling me what a wonderful world it is to not have multiple zones. It just isn't going to happen for a long long time. The multiple-zone kernel is the case we need to care about most by a very large margin indeed. Single-zone is an infinitesimal corner-case. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
