mlel...@serpens.de (Michael van Elst) writes: > malloc doesn't use the "data segment", so that limit doesn't apply to it. > > -d the data segment size of a process (kilobytes) > > RLIMIT_DATA The maximum size (in bytes) of the data segment for a > process; this defines how far a program may extend its > break with the sbrk(2) system call.
Thanks. So that solves why "ulimit -d" doesn't do what someone would expect it to do. > You can try sbrk(2), it should still obey the data segment size (and > may fail if you use it concurrently with malloc()). Sure, but my real goal is to have a memory limit that works, so that I can test that software isn't unreasonably piggy, and to protect the system. > "max memory size" is about physical memory usage and isn't a hard limit. > > -m the total physical memory that can be in use by a > process (kilobytes) > > RLIMIT_RSS The maximum size (in bytes) to which a process's resident > set size may grow. This imposes a limit on the amount of > physical memory to be given to a process; if memory is > tight, the system will prefer to take memory from > processes that are exceeding their declared resident set > size. Interesting, but that seems to be a NetBSD extension. Looking at POSIX, -m is not defined: https://pubs.opengroup.org/onlinepubs/9799919799/ but setrlimit defines RLIMIT_AS (and not RLIMIT_RSS): https://pubs.opengroup.org/onlinepubs/9799919799/functions/getrlimit.html Our shell has -m and -v, both not specified by POSIX, and these therefore must be about RLIMIT_RSS and RLIMIT_AS respectively. > Things were much easier when these limits were invented, in particular > without multithreading and shared libraries, a single heap (the > "data segment") was sufficient for all memory allocations. Sure, but it's really surprising that POSIX does not define a way to limit total usage. My test program can allocate 53548 kB, when total vsize is 200000 kB $ ulimit -v 200000 $ ./test-limits 53548 so this does limit memory usage. Thanks for making me realize that "memory" in -m is pages allocated to real memory.
