[RFC] mm: why cat /proc/pid/smaps | grep Rss is different from cat /proc/pid/statm?

From	Xishi Qiu <qiuxishi@huawei.com>
Newsgroups	linux.kernel
Subject	[RFC] mm: why cat /proc/pid/smaps \| grep Rss is different from cat /proc/pid/statm?
Date	2016-03-22 15:00 +0100
Message-ID	<rfv0K-5cK-11@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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[root@localhost c_test]# cat /proc/3948/smaps | grep Rss
Rss:                   4 kB
Rss:                   4 kB
Rss:                   4 kB
Rss:                 796 kB
Rss:                   0 kB
Rss:                  16 kB
Rss:                   8 kB
Rss:                  12 kB
Rss:                 132 kB
Rss:                  12 kB
Rss:                   4 kB
Rss:                   4 kB
Rss:                   4 kB
Rss:                   4 kB
Rss:                  12 kB
Rss:                   0 kB
Rss:                   4 kB
Rss:                   0 kB
[root@localhost c_test]# cat /proc/3948/statm
1042 173 154 1 0 48 0

173 means Rss is 173*4kb=692kb, right?
so why it is different from the sum(1020kb) of "cat /proc/pid/smaps | grep Rss"?

my test code is
...
int main()
{
	sleep(1000);
	return 0;
}

the kernel version is v4.1

Thanks,
Xishi Qiu

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[RFC] mm: why cat /proc/pid/smaps | grep Rss is different from cat  /proc/pid/statm? Xishi Qiu <qiuxishi@huawei.com> - 2016-03-22 15:00 +0100
  Re: [RFC] mm: why cat /proc/pid/smaps | grep Rss is different from  cat /proc/pid/statm? Xishi Qiu <qiuxishi@huawei.com> - 2016-03-30 09:20 +0200
    Re: [RFC] mm: why cat /proc/pid/smaps | grep Rss is different from  cat /proc/pid/statm? Xishi Qiu <qiuxishi@huawei.com> - 2016-03-30 11:50 +0200

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