Hi Kirill! I recently read the LWN article on your and your colleagues work to add five-level page table support for x86 to the Linux kernel [1] and I got your email address from the last patch of the series. Since this extends the address space beyond 48-bits, as you may know, it will cause potential headaches with Javascript engines which use tagged pointers. On SPARC, the virtual address space already extends to 52 bits and we are running into these very issues with Javascript engines on SPARC. Now, a possible way to mitigate this problem would be to pass the "hint" parameter to mmap() in order to tell the kernel not to allocate memory beyond the 48 bits address space. Unfortunately, on Linux this will only work when the area pointed to by "hint" is unallocated which means one cannot simply use a hardcoded "hint" to mitigate this problem. However, since this trick still works on NetBSD and used to work on Linux [3], I was wondering whether there are plans to bring back this behavior to mmap() in Linux. Currently, people are using ugly work-arounds [4] to address this problem which involve a manual iteration over memory blocks and basically implementing another allocator in the user space application. Thanks, Adrian > [1] https://lwn.net/Articles/717293/ > [2] https://lwn.net/Articles/717300/ > [3] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824449#22 > [4] https://hg.mozilla.org/mozilla-central/rev/dfaafbaaa291 -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer - glaubitz@xxxxxxxxxx `. `' Freie Universitaet Berlin - glaubitz@xxxxxxxxxxxxxxxxxxx `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
