Simple memory locking example

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Simple memory locking example

This is a simple example for handling memory locking.

   #include <stdio.h>
   #include <sys/mman.h> // Needed for mlockall()
   #include <unistd.h> // needed for sysconf(int name);
   #include <malloc.h>
   #include <sys/time.h> // needed for getrusage
   #include <sys/resource.h> // needed for getrusage
#define SOMESIZE (100*1024) // 100kB
int main(int argc, char* argv[]) { // Allocate some memory int i, page_size; char* buffer; struct rusage usage;
// Now lock all current and future pages from preventing of being paged if (mlockall(MCL_CURRENT | MCL_FUTURE )) { perror("mlockall failed:"); }
page_size = sysconf(_SC_PAGESIZE); buffer = malloc(SOMESIZE);
// Touch each page in this piece of memory to get it mapped into RAM for (i=0; i < SOMESIZE; i+=page_size) { // Each write to this buffer will generate a pagefault. // Once the pagefault is handled a page will be locked in memory and never // given back to the system. buffer[i] = 0; // print the number of major and minor pagefaults this application has triggered getrusage(RUSAGE_SELF, &usage); printf("Major-pagefaults:%d, Minor Pagefaults:%d\n", usage.ru_majflt, usage.ru_minflt); } // buffer is never released, or swapped, so using it from now will never lead to any pagefault
//<do your RT-thing>
return 0; }

Notice that for this application you have to be 'root' to function properly. In fact: you only need the capability called 'CAP_IPC_LOCK' Notice also the difference between running this program with and without using the mlockall() call. Tip: Also run this application when there is no free RAM in the system, and see that the number of initial major pagefaults increases.

During runtime the getrusage() can be used to detect if the running RT application has been trapped by any new pagefaults.


Remy Bohmer


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Revision 1 2008-01-15
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