On Tue, Apr 29, 2014 at 12:35:34PM +0100, Arnd Bergmann wrote: > On Tuesday 29 April 2014 12:19:46 Will Deacon wrote: > > On Sat, Apr 26, 2014 at 03:12:40AM +0100, Jianguo Wu wrote: > > > On 2014/1/3 8:47, Russell King - ARM Linux wrote: > > > > ARM can only branch relatively within +/- 32MB. Hence, with a module > > > > space of 16MB, modules can reach up to a maximum 16MB into the direct- > > > > mapped kernel image. As module space increases in size, so that figure > > > > decreases. So, if module space were to be 40MB, the maximum size of the > > > > kernel binary would be 8MB. > > > > > > > > > > Hi Russell ,Arnd or Will, > > > > > > I encountered the same situation in arm64, I loaded 80+ modules in arm64, and > > > run out of module address space(64M). Why the module space is restricted to 64M, > > > can it be expanded? > > > > The module space is restricted to 64M on AArch64 because the range of the BL > > instruction is += 128M. In order to call kernel functions, we need to ensure > > that this range is large enough and therefore place the modules 64M below the > > kernel text, allowing 64M for modules and 64M for the kernel text. We could > > probably improve this a bit by assuming a maximum size for the kernel text. > > > > If we want to remove the problem altogether, we'd need to hack the module > > loader to insert trampolines (fiddly) or somehow persuade the tools to use > > indirect branches (BLR) for all calls (inefficient). > > Well, there might also be a bug involved. Loading 80 modules should never > take up 64MB. The typical size of a loadable module should be a few dozen > kilobytes, although we have a few modules that are hundreds of kilobytes. > > Jianguo Wu, can you send the defconfig you were using? Did you have > some debugging option enabled that increased the module size? If 64K pages are in use we could end up with a tonne of fragmentation but yes, worth looking at the .config. Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>