On Thu, Apr 10, 2008 at 8:03 PM, Gilles Chanteperdrix
<[EMAIL PROTECTED]> wrote:
>
> On Thu, Apr 10, 2008 at 7:52 PM, jeff koftinoff <[EMAIL PROTECTED]> wrote:
> > Gilles Chanteperdrix wrote:
> >
> > >
> > > It looks we are wrong. The main thread stack remains allocated
> > > on-demand, even though the process is mlocked. It must be some recent
> > > kernel evolution
> > >
> >
> > Hmm.. interesting. What is the best way to make sure all my stacks are
> not
> > allocated on-demand?
>
> Find attached the example I used to read the stack size of an mlocked
> process.
>
> You can run it on your target to see if you get the same result as me.
>
> Now, I suspect this on-demand allocation only exists for the main
> thread stack, I will run further tests to confirm this. So, you may:
> - decide not to use the main thread for real-time duties
> - memset a large buffer on stack to force the kernel to commit memory.
Forgot the attachment, but here is a better one, which prints the main
thread stack size as well as a newly created thread stack size. It
shows that, at least in my configuration, only the main thread stack
mapping is grown on-demand.
--
Gilles
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <string.h>
#include <pthread.h>
long get_stack_size(unsigned long stackptr)
{
char *line = NULL;
size_t linesz;
FILE *file;
int len;
file = fopen("/proc/self/maps", "r");
if (!file) {
perror("fopen(/proc/self/maps)");
exit(EXIT_FAILURE);
}
while ((len = getline(&line, &linesz, file)) != -1) {
unsigned long map_start, map_end;
/* Remove trailing \r\n (if any) */
while (line[len - 1] == '\n' || line[len - 1] == '\r')
line[--len] = '\0';
if (sscanf(line, "%lx-%lx", &map_start, &map_end) < 2) {
perror("sscanf");
exit(EXIT_FAILURE);
}
if ((unsigned) (stackptr - map_start) >= (map_end - map_start))
continue;
free(line);
fclose(file);
return map_end - map_start;
}
if (line)
free(line);
fclose(file);
fprintf(stderr, "Could not find stack in /proc/self/maps\n");
exit(EXIT_FAILURE);
}
unsigned long threadstack;
void *thread(void *cookie)
{
unsigned dummy;
threadstack = (unsigned long) &dummy;
pause();
return cookie;
}
int main(void)
{
pthread_t tid;
int err;
if (mlockall(MCL_CURRENT | MCL_FUTURE)) {
perror("mlockall");
exit(EXIT_FAILURE);
}
if ((err = pthread_create(&tid, NULL, thread, NULL))) {
fprintf(stderr, "pthread_create: %s\n", strerror(err));
exit(EXIT_FAILURE);
}
sleep(1);
printf("stack: %ldK\n", get_stack_size((unsigned long) &tid) / 1024);
printf("thread stack: %ldK\n", get_stack_size(threadstack) / 1024);
return 0;
}
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