linux-kernel - Re: [PATCH] selftests/vm: Add test to validate mirror functionality with mremap

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Date:   Thu, 20 Jul 2017 16:19:31 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org
Subject: Re: [PATCH] selftests/vm: Add test to validate mirror functionality
 with mremap

On 07/20/2017 02:36 AM, Anshuman Khandual wrote:
> This adds a test to validate mirror functionality with mremap()
> system call on shared anon mappings.
> 
> Suggested-by: Mike Kravetz <mike.kravetz@...cle.com>
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> ---
>  tools/testing/selftests/vm/Makefile                |  1 +
>  .../selftests/vm/mremap_mirror_shared_anon.c       | 54 ++++++++++++++++++++++

This may be a better fit in LTP where there are already several other
mremap tests.  I honestly do not know the best place for such a test.

>  2 files changed, 55 insertions(+)
>  create mode 100644 tools/testing/selftests/vm/mremap_mirror_shared_anon.c
> 
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index cbb29e4..11657ff5 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -17,6 +17,7 @@ TEST_GEN_FILES += transhuge-stress
>  TEST_GEN_FILES += userfaultfd
>  TEST_GEN_FILES += mlock-random-test
>  TEST_GEN_FILES += virtual_address_range
> +TEST_GEN_FILES += mremap_mirror_shared_anon
>  
>  TEST_PROGS := run_vmtests
>  
> diff --git a/tools/testing/selftests/vm/mremap_mirror_shared_anon.c b/tools/testing/selftests/vm/mremap_mirror_shared_anon.c
> new file mode 100644
> index 0000000..b0adbb2
> --- /dev/null
> +++ b/tools/testing/selftests/vm/mremap_mirror_shared_anon.c
> @@ -0,0 +1,54 @@
> +/*
> + * Test to verify mirror functionality with mremap() system
> + * call for shared anon mappings.
> + *
> + * Copyright (C) 2017 Anshuman Khandual, IBM Corporation
> + *
> + * Licensed under GPL V2
> + */
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <errno.h>
> +#include <sys/mman.h>
> +#include <sys/time.h>
> +
> +#define PATTERN		0xbe
> +#define ALLOC_SIZE	0x10000UL /* Works for 64K and 4K pages */

Why hardcode?  You could use sysconf to get page size and use some
multiple of that.

> +
> +int test_mirror(char *old, char *new, unsigned long size)
> +{
> +	unsigned long i;
> +
> +	for (i = 0; i < size; i++) {
> +		if (new[i] != old[i]) {
> +			printf("Mismatch at new[%lu] expected "
> +				"%d received %d\n", i, old[i], new[i]);
> +			return 1;
> +		}
> +	}
> +	return 0;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	char *ptr, *mirror_ptr;
> +
> +	ptr = mmap(NULL, ALLOC_SIZE, PROT_READ | PROT_WRITE,
> +			MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> +	if (ptr == MAP_FAILED) {
> +		perror("map() failed");
> +		return -1;
> +	}
> +	memset(ptr, PATTERN, ALLOC_SIZE);
> +
> +	mirror_ptr =  (char *) mremap(ptr, 0, ALLOC_SIZE, 1);

Why hardcode 1?  You really want the MREMAP_MAYMOVE flag.  Right?

> +	if (mirror_ptr == MAP_FAILED) {
> +		perror("mremap() failed");
> +		return -1;
> +	}
> +
> +	if (test_mirror(ptr, mirror_ptr, ALLOC_SIZE))
> +		return 1;
> +	return 0;
> +}

You may want to expand the test to make sure mremap(old_size == 0)
fails for private mappings.  Of course, this assumes my proposed
patch gets in.  Until then, it will succeed and create a new unrelated
mapping.

-- 
Mike Kravetz