linux-kernel - Re: [Question] Mlocked count will not be decreased

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Date:   Wed, 24 May 2017 07:04:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, zhongjiang <zhongjiang@...wei.com>,
        Qiuxishi <qiuxishi@...wei.com>,
        Yisheng Xie <xieyisheng1@...wei.com>
Subject: Re: [Question] Mlocked count will not be decreased

Kefeng Wang wrote:
> Hi All,
> 
> Mlocked in meminfo will be increasing with an small testcase, and never be released in mainline,
> here is a testcase[1] to reproduce the issue, but the centos7.2/7.3 will not increase.
> 
> Is it normal?

I confirmed your problem also occurs in Linux 4.11 using below testcase.
MemFree is not decreasing while Mlocked is increasing.
Thus, it seems to be statistics accounting bug.

----------
#include <sys/mman.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char ** argv)
{
	int i;
	for (i = 0; i < 128; i++)
		if (fork() == 0) {
			malloc(1048576);
			while (1) {
				mlockall(MCL_CURRENT | MCL_FUTURE);
				munlockall();
			}
		}
	return 0;
}
----------