Here's a simple program to trigger the issue with /proc/<pid>/maps.
Thanks,
Calvin
/* Simple program to reproduce O(N^2) behavior reading /proc/<pid>/maps
*
* Example on a random server:
*
* $ ./map_repro 0
* Spawning 0 threads
* Reading /proc/self/maps... read 2189 bytes in 1 syscalls in 33us!
* $ ./map_repro 10
* Spawning 10 threads
* Reading /proc/self/maps... read 3539 bytes in 1 syscalls in 55us!
* $ ./map_repro 100
* Spawning 100 threads
* Reading /proc/self/maps... read 15689 bytes in 4 syscalls in 373us!
* $ ./map_repro 1000
* Spawning 1000 threads
* Reading /proc/self/maps... read 137189 bytes in 34 syscalls in 32376us!
* $ ./map_repro 2000
* Spawning 2000 threads
* Reading /proc/self/maps... read 272189 bytes in 68 syscalls in 119980us!
* $ ./map_repro 4000
* Spawning 4000 threads
* Reading /proc/self/maps... read 544912 bytes in 134 syscalls in
712200us!
* $ ./map_repro 8000
* Spawning 8000 threads
* Reading /proc/self/maps... read 1090189 bytes in 268 syscalls in
3650718us!
* $ ./map_repro 16000
* Spawning 16000 threads
* Reading /proc/self/maps... read 2178189 bytes in 534 syscalls in
42701311us!
*/
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <limits.h>
#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <fcntl.h>
static char buf[65536] = {0};
static void time_maps_read(void)
{
struct timespec then, now;
long usec_elapsed;
int ret, fd;
int count = 0;
int rd = 0;
fd = open("/proc/self/maps", O_RDONLY);
if (fd == -1) {
printf("Couldn't open /proc/self/maps, bailing...\n");
return;
}
printf("Reading /proc/self/maps... ");
ret = clock_gettime(CLOCK_MONOTONIC, &then);
while (1) {
ret = read(fd, &buf, 65536);
if (!ret || ret == -1)
break;
rd += ret;
count++;
}
ret = clock_gettime(CLOCK_MONOTONIC, &now);
usec_elapsed = (now.tv_sec - then.tv_sec) * 1000000L;
usec_elapsed += (now.tv_nsec - then.tv_nsec) / 1000L;
printf("read %d bytes in %d syscalls in %ldus!\n", rd, count,
usec_elapsed);
close(fd);
}
static void *do_nothing_forever(void *unused)
{
while (1)
sleep(60);
return NULL;
}
int main(int args, char **argv)
{
int i, ret, threads_to_spawn = 0;
pthread_t tmp;
if (args != 1) {
threads_to_spawn = atoi(argv[1]);
printf("Spawning %d threads\n", threads_to_spawn);
}
for (i = 0; i < threads_to_spawn; i++) {
ret = pthread_create(&tmp, NULL, do_nothing_forever, NULL);
if (ret)
printf("Thread %d failed to spawn?\n", i);
}
time_maps_read();
return 0;
}
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