On Mon, Mar 11, 2013 at 12:04:38PM -0700, H. Peter Anvin wrote: > On 03/11/2013 12:02 PM, Vivek Goyal wrote: > >> > >> What is the purpose of reserving that kind of memory below 896 MB? If > >> you have a 32-bit system, it will likely be useless since you are > >> robbing the primary of most of lowmem, on a 64-bit system 896 MB is not > >> a magic value in any way...? > > > > Actually I am not sure where did 896MB magic value had come from for > > x86_64 so far. I assumed that it was some kexec-tools limitation so > > first trying 896MB will preserve working with old kexec-tools. If it > > was some kernel limitation, then I agree it should not be required anymore. > > > > I do remember that old pugatory had 2G limit. So may be we can first > > try reserve with-in first 2G, then with-in first 4G and then above > > 4G. (Assuming 896M was not kexec-tools limitation and had something > > to do with kernel/initramfs). > > > > It is obvious where it *originated* from... it is the *default* (but not > necessarily the actual!) HIGHMEM crossover point on x86-32. >
On x86-32, max addr limit is 512M. 896M limit is on x86_64. So it probably came from somewhere else. Also always reserving at high memory cuts down on what kind of bzImage can be booted from that address. For example, x86_32bit kernels. Hence reserving at low addresses enables booting more type of images without rebooting. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
