This is a memory monitoring interface implemented with reference to Linux's PSI (Pressure Stall Information),
which can send notifications when the system's remaining memory is below the threshold.
The following example code sets two different thresholds.
When the system memory is below 10MB, a notification is triggered.
When the system memory is below 20 MB, a notification (POLLPRI event) is triggered every 1s.
```
int main(int argc, FAR char *argv[])
{
struct pollfd fds[2];
int ret;
if (argc == 2)
{
char *ptr = malloc(1024*1024*atoi(argv[1]));
printf("Allocating %d MB\n", atoi(argv[1]));
ptr[0] = 0;
return 0;
}
fds[0].fd = open("/proc/pressure/memory", O_RDWR);
fds[1].fd = open("/proc/pressure/memory", O_RDWR);
fds[0].events = POLLPRI;
fds[1].events = POLLPRI;
dprintf(fds[0].fd, "%llu -1", 1024LLU*1024 * 10);
dprintf(fds[1].fd, "%llu 1000000", 1024LLU*1024 * 20);
while (1)
{
ret = poll(fds, 2, -1);
if (ret > 0)
{
printf("Memory pressure: POLLPRI, %d\n", ret);
}
}
return 0;
}
```
https://docs.kernel.org/accounting/psi.html
Signed-off-by: yinshengkai <yinshengkai@xiaomi.com>
