From: kernelnewbies-bounces@kernelnewbies.org [mailto:kernelnewbies-bounces@kernelnewbies.org] On Behalf Of Kevin O'Gorman Sent: Monday, August 18, 2014 8:15 AM To: kernelnewbies@kernelnewbies.org Subject: Why I can't map memory with mmap maybe someone here can help me figure out how to map a big (really big) work area and lock it in memory. I wrote a little test program to try this out, and it fails. As a regular user, perror() tells me some "resource is temporarily unavailable". As root, it says it "cannot allocate memory". I'm only asking for 1 byte. What's the problem? BTW it also fails if it asks for a mibibyte (1<<20). Here's the whole program /** * @file * <pre>"Find out the limits on locked memory" * Last Modified: Mon Aug 18 07:31:01 PDT 2014</pre> * @author Kevin O'Gorman */ #define _GNU_SOURCE /* enable some of the mmap flags */ #include <unistd.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <sys/mman.h> int main(int argc, char *argv[]) { void *where; size_t length = 1; where = mmap(NULL, length, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_LOCKED | MAP_POPULATE, -1, 0); if (where != MAP_FAILED) { printf("Mapped at %p\n", where); } else { perror("Mapping failed"); } return EXIT_SUCCESS; } I'm pretty sure you need to pass the file descriptor of an open file or device as the fd (second parameter from the end). -1 is not a valid fd. Jeff Haran