Expedited memory reclaim from killed processes

Expedited memory reclaim from killed processes

I believe opting-in to overcommit is already possible, with the MAP_NORESERVE flag - which essentially says that the mapped range can be overcommitted, and defines behaviour if you write to it when there is insufficient commit available.

There's a bit of a chicken-and-egg problem here, though - heuristic overcommit exists because it's easier for system administrators to tell the OS to lie to applications that demand too much memory than it is for those self-same administrators to have the applications retooled to handle overcommit sensibly.

And even if you are retooling applications, it's often easier to simply turn on features like Kernel Same-page Merging to cope with duplication (e.g. in the Suricata ruleset in-memory form) than it is to handle al the fun that comes from opt-in overcommit.

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static void do_brk(int unused)
{
    sbrk(128);
}

int main(int argc, char **argv)
{
    unsigned *p;

    signal(SIGSEGV, do_brk);

    p = sbrk(0);
    *p = atoi(argv[1]);
    printf("%u\n", *p);
    
    return 0;
}