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

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Message-Id: <f1d97d49-df0a-4da9-520e-cc55e3d635c0@linux.vnet.ibm.com>
Date:   Fri, 21 Jul 2017 16:08:23 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        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 07/21/2017 04:49 AM, Mike Kravetz wrote:
> 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.

Yeah but these days self tests try to target smaller functional
tests which can run quickly and validate something, hence thought
this may be appropriate as a self 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.

Sure, will do 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?

Right, missed that. My bad.

> 
>> +	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.

Even without your patch, the data in the new mapping still does
not match the original one. Anyway, will accommodate private
anon mapping as well.