On Friday, December 16, 2016 4:25:14 PM CET Yury Norov wrote: > On Sun, Dec 11, 2016 at 03:59:01PM +0100, Arnd Bergmann wrote: > > On Sunday, December 11, 2016 6:26:42 PM CET Yury Norov wrote: > > > Also fix related interfaces > > > > > > Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > > > > Thanks Yury for the demonstration. I think this would put the nail > > in the coffin of the idea of mmap64 even for Pavel, who didn't > > seem convinced already. > > > > Changing all those interfaces and structure, struct page in particular, > > is clearly too costly for any advantage we might have otherwise > > gained. > > > > Arnd > > To be complete, we have 3 options: > 1 leave things as is. 32-bit architectures will have no option to > mmap big offsets, and no one cares - as usual. > 2 add mmap64() for compat arches only. This way we don't need patch > 3, and arches like aarch32 or aarch64/ilp32 will enjoy true 64-bit > offsets. > 3 introduce CONFIG_64_BIT_PGOFF_T, and let Pavel enable it if he has > to work with big files on 32-bit arches. > > The most realistic approach for me is 1 because I never heard about > 64-bit pgoff_t requests, except Pavel's one. Thinking about > aarch64/ilp32, we probably need second approach. This is only 2 simple > patches that are already there, and one patch in glibc. It will let > 32-bit software work in 64-bit environment more smoothly. Cavium > people should be completely satisfied with 2. Agreed: If there is a serious request from Cavium or Huawei (which are also very interested in this feature) and a specific use case, we can still do 2 easily. > Third is more looking like research exercise than something we need > in practice. Right. > The only thing that makes me sad is that we proudly declare 64-bit > off_t in new 32-bit ABIs but in fact we lie, at least in this > specific case. We should add corresponding checks on glibc side at > least. It's also simple. Well, the only thing we are really saying there is that we support more than 32-bit, and that the ABI uses 64-bit. Actually doing 64-bit offsets within (very sparse) files probably also fails on 64-bit architectures, at least on some file systems. Arnd -- 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
