linux-kernel - Re: [PATCH] mm/oom_kill.c: don't kill TASK

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Date:	Tue, 22 Sep 2015 14:33:47 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	rientjes@...gle.com
Cc:	mhocko@...nel.org, cl@...ux.com, oleg@...hat.com,
	kwalker@...hat.com, akpm@...ux-foundation.org, hannes@...xchg.org,
	vdavydov@...allels.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, skozina@...hat.com
Subject: Re: [PATCH] mm/oom_kill.c: don't kill TASK_UNINTERRUPTIBLE tasks

David Rientjes wrote:
> Your proposal, which I mostly agree with, tries to kill additional 
> processes so that they allocate and drop the lock that the original victim 
> depends on.  My approach, from 
> http://marc.info/?l=linux-kernel&m=144010444913702, is the same, but 
> without the killing.  It's unecessary to kill every process on the system 
> that is depending on the same lock, and we can't know which processes are 
> stalling on that lock and which are not.

Would you try your approach with below program?
(My reproducers are tested on XFS on a VM with 4 CPUs / 2048MB RAM.)

---------- oom-depleter3.c start ----------
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sched.h>

static int zero_fd = EOF;
static char *buf = NULL;
static unsigned long size = 0;

static int dummy(void *unused)
{
	static char buffer[4096] = { };
	int fd = open("/tmp/file", O_WRONLY | O_CREAT | O_APPEND, 0600);
	while (write(fd, buffer, sizeof(buffer) == sizeof(buffer)) &&
	       fsync(fd) == 0);
	return 0;
}

static int trigger(void *unused)
{
	read(zero_fd, buf, size); /* Will cause OOM due to overcommit */
	return 0;
}

int main(int argc, char *argv[])
{
        unsigned long i;
	zero_fd = open("/dev/zero", O_RDONLY);
	for (size = 1048576; size < 512UL * (1 << 30); size <<= 1) {
		char *cp = realloc(buf, size);
		if (!cp) {
			size >>= 1;
			break;
		}
		buf = cp;
	}
	/*
	 * Create many child threads in order to enlarge time lag between
	 * the OOM killer sets TIF_MEMDIE to thread group leader and
	 * the OOM killer sends SIGKILL to that thread.
	 */
	for (i = 0; i < 1000; i++) {
		clone(dummy, malloc(1024) + 1024, CLONE_SIGHAND | CLONE_VM,
		      NULL);
	}
	/* Let a child thread trigger the OOM killer. */
	clone(trigger, malloc(4096)+ 4096, CLONE_SIGHAND | CLONE_VM, NULL);
	/* Deplete all memory reserve using the time lag. */
	for (i = size; i; i -= 4096)
		buf[i - 1] = 1;
	return * (char *) NULL; /* Kill all threads. */
}
---------- oom-depleter3.c end ----------

uptime > 350 of http://I-love.SAKURA.ne.jp/tmp/serial-20150922-1.txt.xz
shows that the memory reserves completely depleted and
uptime > 42 of http://I-love.SAKURA.ne.jp/tmp/serial-20150922-2.txt.xz
shows that the memory reserves was not used at all.
Is this result what you expected?
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