On Tue 16-08-16 12:46:51, Robert Foss wrote:
[...]
> $ /usr/bin/time -v -p zsh -c "repeat 25 { awk '/^Rss/{rss+=\$2}
> /^Pss/{pss+=\$2} END {printf \"rss:%d pss:%d\n\", rss, pss}\'
> /proc/5025/smaps }"
> [...]
> Command being timed: "zsh -c repeat 25 { awk '/^Rss/{rss+=$2}
> /^Pss/{pss+=$2} END {printf "rss:%d pss:%d\n", rss, pss}\' /proc/5025/smaps
> }"
> User time (seconds): 0.37
> System time (seconds): 0.45
> Percent of CPU this job got: 92%
> Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.89
This is really unexpected. Where is the user time spent? Anyway, rather
than measuring some random processes I've tried to measure something
resembling the worst case. So I've created a simple program to mmap as
much as possible:
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
while (mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_ANON|MAP_SHARED|MAP_POPULATE, -1, 0) != MAP_FAILED)
;
printf("pid:%d\n", getpid());
pause();
return 0;
}
so depending on /proc/sys/vm/max_map_count you will get the maximum
possible mmaps. I am using a default so 65k mappings. Then I have
retried your 25x file parsing:
$ cat s.sh
#!/bin/sh
pid=$1
for i in $(seq 25)
do
awk '/^Rss/{rss+=$2} /^Pss/{pss+=$2} END {printf "rss:%d pss:%d\n", rss, pss}' /proc/$pid/smaps
done
But I am getting different results from you:
$ awk '/^[0-9a-f]/{print}' /proc/14808/smaps | wc -l
65532
[...]
Command being timed: "sh s.sh 14808"
User time (seconds): 0.00
System time (seconds): 20.10
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:20.20
The results are stable when I try multiple times, in fact there
shouldn't be any reason for them not to be. Then I went on to increase
max_map_count to 250k and that behaves consistently:
$ awk '/^[0-9a-f]/{print}' /proc/16093/smaps | wc -l
250002
[...]
Command being timed: "sh s.sh 16093"
User time (seconds): 0.00
System time (seconds): 77.93
Percent of CPU this job got: 98%
Elapsed (wall clock) time (h:mm:ss or m:ss): 1:19.09
So with a reasonable user space the parsing is really not all that time
consuming wrt. smaps handling. That being said I am still very skeptical
about a dedicated proc file which accomplishes what userspace can done
in a trivial way.
--
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
