ThreadSanitizer doesn't work with memory overcommit disabled

[zackw]

On Linux, if memory overcommit has been disabled (sysctl -w vm.overcommit_memory=2), all programs compiled with -fsanitize=thread crash on startup with an error message...

==363640==ERROR: ThreadSanitizer failed to allocate 0x200000000000 (35184372088832) bytes at address 100000000000 (errno: 12)
FATAL: ThreadSanitizer can not mmap the shadow memory
FATAL: Make sure to compile with -fPIE and to link with -pie.

... that indicates ThreadSanitizer attempted to allocate 32 terabytes of RAM. That's not a reasonable amount of memory to expect a developer workstation to have.

Please change ThreadSanitizer so that it only allocates shadow memory proportional to the amount of RAM that the program actually uses. You can probably use MAP_NORESERVE to allocate a range of address space without also allocating RAM.