[Devel] Re: [BUGFIX][RFC][PATCH][only -mm] FIX memory leak in memory cgroup vs. page migration [0/1]

[KAMEZAWA Hiroyuki]

On Tue, 02 Oct 2007 19:04:15 +0530
Balbir Singh <balbir at linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > Current implementation of memory cgroup controller does following in migration.
> > 
> > 1. uncharge when unmapped.
> > 2. charge again when remapped.
> > 
> > Consider migrate a page from OLD to NEW.
> > 
> > In following case, memory (for page_cgroup) will leak.
> > 
> > 1. charge OLD page as page-cache. (charge = 1
> > 2. A process mmap OLD page. (chage + 1 = 2)
> > 3. A process migrates it.
> >    try_to_unmap(OLD) (charge - 1 = 1)
> >    replace OLD with NEW
> >    remove_migration_pte(NEW) (New is newly charged.)
> >    discard OLD page. (page_cgroup for OLD page is not reclaimed.)
> > 
> 
> Interesting test scenario, I'll try and reproduce the problem here.
> Why does discard OLD page not reclaim page_cgroup?
Just because OLD page is not page-cache at discarding. (it is replaced with NEW page)


>
> > [root at drpq kamezawa]# ./migrate_test 512Mfile 1 &
> > [1] 4108
> > #At the end of migration,
> 
> Where can I find migrate_test?
> 
here, (just I wrote for this test. works on my RHEL5/2.6.18-rc8-mm2/ia64 NUMA box)
This program doesn't check 'where is file cache ?' before migration. So please
check it by yourself before run.
==

#include <stdio.h>
#include <stdlib.h>
#include <syscall.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <numaif.h>
#include <unistd.h>

#define PAGESIZE	(16384)

static inline int move_pages(pid_t pid, unsigned long nr_pages,
		const void **address,
		const int *nodes, int *status, int flags)
{
	return syscall(SYS_move_pages, pid, nr_pages, address,
			nodes, status, flags);
}
/*
 * migrate_test.c -- mmap file and migrate it to specified node.
 * %migrate_task file nodeid
 *
 */

int main(int argc, char *argv[])
{
	int ret, fd, val, node[1], status[1];
	char *addr, *c;
	unsigned long size, nr_pages, pos;
	struct stat statbuf;
	void *address[1];
	int target;

	if (argc != 3) {
		fprintf(stderr,"usage: migrate_test file node\n");
		exit(0);
	}
	target = atoi(argv[2]);

	fd = open(argv[1], O_RDONLY);
	if (fd < 0) {
		perror("open");
		exit(1);
	}

	ret = fstat(fd, &statbuf);
	if (ret < 0) {
		perror("fstat");
		exit(1);
	}

	size = statbuf.st_size;
	nr_pages = size/PAGESIZE;
	size = nr_pages * PAGESIZE;

	addr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);

	if (addr == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}
	/* Touch all */
	for (pos = 0; pos < nr_pages; pos++) {
		c = addr + pos * PAGESIZE;
		val += *c;
	}
	/* Move Pages */
	for (pos = 0; pos < nr_pages; pos++) {
		node[0] = target;
		status[0] = 0;
		address[0] = addr + pos * PAGESIZE;
		ret = move_pages(0, 1, address, node, status,
				MPOL_MF_MOVE_ALL);
		if (ret) {
			perror("move_pages");
		}
#if 1
		printf("pos %d %p %d %d\n",pos, address[0], node[0], status[0]);
#endif
	}
	/* Touch all again....maybe unnecessary.*/
	for (pos = 0; pos < nr_pages; pos++) {
		c = addr + pos * PAGESIZE;
		val += *c;
	}
	while (1) {
		/* mmap until killed */
		pause();
	}
	printf("val %d\n",val);
	return 0;
}



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