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From: Grazvydas Ignotas <notasas@gmail.com>
To: linux-kernel@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Grazvydas Ignotas <notasas@gmail.com>
Subject: remap_file_pages regression
Date: Mon, 15 Feb 2016 03:32:55 +0200
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Hi,

since remap_file_pages() rework the following simple program fails.
I haven't actually bisected this, only know it worked on 3.19 at least
(I bought a new system now and need 4.2+ for hardware support). If you
are curious, the program is an emulator and is using remap_file_pages()
to implement memory mirroring efficiently (and to remap things during
run time).

Grazvydas

====%<===

#define _GNU_SOURCE
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>

#define SIZE	(4096 * 3)

int main(int argc, char **argv)
{
	unsigned long *p;
	long i;

	p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
			MAP_SHARED | MAP_ANONYMOUS, -1, 0);
	if (p == MAP_FAILED) {
		perror("mmap");
		return -1;
	}

	for (i = 0; i < SIZE / 4096; i++)
		p[i * 4096 / sizeof(*p)] = i;

	if (remap_file_pages(p, 4096, 0, 1, 0)) {
		perror("remap_file_pages");
		return -1;
	}

	if (remap_file_pages(p, 4096 * 2, 0, 1, 0)) {
		perror("remap_file_pages");
		return -1;
	}

	assert(p[0] == 1);

	munmap(p, SIZE);

	return 0;
}