Hello All,
When I did some testing to check thp's performance, the following
strange action occurred:
when a process try to allocate 500+(or other large value)
anonymous hugepage, the 'khugepaged' thread will stop to
scan vma. the testing system has 2Gb RAM, and the thp
enabled value is 'always', set 0 to 'scan_sleep_millisecs'
you can use the following steps to confirm the issue:
---------------- example code ------------
/* file test_thp.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
int main(int argc, char *argv[])
{
int nr_thps = 1000, ret = 0;
unsigned long hugepagesize, size;
void *addr;
hugepagesize = (1UL << 21);
if (argc == 2)
nr_thps = atoi(argv[1]);
printf("try to allocate %d transparent hugepages\n", nr_thps);
size = (unsigned long)nr_thps * hugepagesize;
ret = posix_memalign(&addr, hugepagesize, size);
if (ret != 0) {
printf("posix_memalign failed\n");
return ret;
}
memset (addr, 10, size);
sleep(50);
return ret;
}
-------- end example code -----------
executing './test_thp 500' in a system with 2GB RAM, the values in
/sys/kernel/mm/transparent_hugepage/khugepaged/* will never change,
you can repeatedly do '# cat /sys/kernel/mm/transparent_hugepage/khugepaged/*'
to check this.
as we know, when we set 0 to
/sys/kernel/mm/transparent_hugepage/khugepaged/scan_sleep_millisecs,
the /sys/kernel/mm/transparent_hugepage/khugepaged/full_to_scans will
increasing at least,
but the actual is opposite, the value is never change, so I checked
'khugepaged' thread,
and found the 'khugepaged' is stopped:
# ps aux | grep -i hugepaged
root 67 10.9 0.0 0 0 ? SN Apr06 172:10 [khugepaged]
^^
also I did the same actions on some large machine, e.g on 16Gb RAM, 1000+
anonymous hugepages
will cause 'khugepaged' stopped, but there are 2Gb+ free memory, why is it? is
that normal?
comments?
--
Thanks,
Zhouping
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