On Thu, 1 Nov 2007, David Miller wrote: > From: Christoph Lameter <clameter@xxxxxxx> > Date: Thu, 1 Nov 2007 06:03:44 -0700 (PDT) > > > In order to make it truly dynamic we would have to virtually map the > > area. vmap? But that reduces performance. > > But it would still be faster than the double-indirection we do now, > right? I think I have an idea how to do this. Its a bit x86_64 specific but here it goes. We define a virtual area of NR_CPUS * 2M areas that are each mapped by a PMD. That means we have a fixed virtual address for each cpus per cpu area. First cpu is at PER_CPU_START Second cpu is at PER_CPU_START + 2M So the per cpu area for cpu n is easily calculated using PER_CPU_START + cpu << 19 without any lookups. On bootup we allocate the 2M pages. After boot is complete we allow the reduction of the size of the per cpu areas . Lets say we only need 128k per cpu. Then the remaining pages will be returned to the page allocator. We create some sysfs thingy were one can see the current reserves of per cpu storage. If one wants to reduce memory then one can write something to that to return the remainder of the memory. - To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
