Sigh... apologies for the HTML. Trying again... On Mon, Feb 20, 2017 at 9:21 PM, Michael Pratt <linux@xxxxxxxx> wrote: > On Fri, Feb 17, 2017 at 3:02 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> On Fri, Feb 17, 2017 at 1:01 PM, Linus Torvalds >> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >>> On Fri, Feb 17, 2017 at 12:12 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >>>> >>>> At the very least, I'd want to see >>>> MAP_FIXED_BUT_DONT_BLOODY_UNMAP_ANYTHING. I *hate* the current >>>> interface. >>> >>> That's unrelated, but I guess w could add a MAP_NOUNMAP flag, and then >>> you can use MAP_FIXED | MAP_NOUNMAP or something. >>> >>> But that has nothing to do with the 47-vs-56 bit issue. >>> >>>> How about MAP_LIMIT where the address passed in is interpreted as an >>>> upper bound instead of a fixed address? >>> >>> Again, that's a unrelated semantic issue. Right now - if you don't >>> pass in MAP_FIXED at all, the "addr" argument is used as a starting >>> value for deciding where to find an unmapped area. But there is no way >>> to specify the end. That would basically be what the process control >>> thing would be (not per-system-call, but per-thread ). >>> >> >> What I'm trying to say is: if we're going to do the route of 48-bit >> limit unless a specific mmap call requests otherwise, can we at least >> have an interface that doesn't suck? I've got a set of patches that I've meant to send out as an RFC for a while that tries to address userspace control of address space layout and covers many of these ideas. There is a new syscall and set of prctls for controlling the "mmap layout" (i.e., get_unmapped_area search range) that look something like this: struct mmap_layout { unsigned long start; unsigned long end; /* * These are equivalent to mmap_legacy_base and mmap_base, * but are not really needed in this proposal. */ unsigned long low_base; unsigned long high_base; unsigned long flags; }; /* For flags */ #define MMAP_TOPDOWN 1 struct layout_mmap_args { unsigned long addr; unsigned long len; unsigned long prot; unsigned long flags; unsigned long fd; unsigned long off; struct mmap_layout layout; }; void *layout_mmap(struct layout_mmap_args *args); int prctl(PR_GET_MMAP_LAYOUT, struct mmap_layout *layout); int prctl(PR_SET_MMAP_LAYOUT, struct mmap_layout *layout); The prctls control the default range that mmap and friends will allocate. For 56-bit user address space, it could default to [mmap_min_addr, 1<<47), as Linus suggests. Applications that want the full address space can increase it to cover the entire range. The layout_mmap syscall allows one-off mappings that fall outside the default layout, and nicely solves the "MAP_FIXED but don't unmap anything problem" by passing an explicit range to check without actually setting MAP_FIXED. This idea is quite similar to the MAX_VADDR + default get_unmapped_area behavior ides, just more generalized to give userspace more control over the ultimate behavior of get_unmapped_area. PS. Apologies if my email client screwed up this message. I didn't have this thread in my client and have tried to import it from another account. -- 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>