linux-kernel - Re: [PATCH V2] selftests/vm: Add tests to validate mirror functionality with mremap

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Message-Id: <32236948-422c-3519-7be3-88527895bf92@linux.vnet.ibm.com>
Date:   Wed, 26 Jul 2017 09:54:26 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, mike.kravetz@...cle.com
Subject: Re: [PATCH V2] selftests/vm: Add tests to validate mirror
 functionality with mremap

On 07/25/2017 07:06 PM, Michal Hocko wrote:
> On Tue 25-07-17 12:06:57, Anshuman Khandual wrote:
> [...]
>> diff --git a/tools/testing/selftests/vm/mremap_mirror_private_anon.c b/tools/testing/selftests/vm/mremap_mirror_private_anon.c
> [...]
>> +	ptr = mmap(NULL, alloc_size, PROT_READ | PROT_WRITE,
>> +			MAP_PRIVATE | 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, MREMAP_MAYMOVE);
>> +	if (mirror_ptr == MAP_FAILED) {
>> +		perror("mremap() failed");
>> +		return -1;
>> +	}
> 
> What is the point of this test? It will break with Mike's patch very
> soon. Btw. it never worked.

It works now. The new 'mirrored' buffer does not have same elements
as that of the original one. Yes, once Mike's patch is merged, it
will fail during the mremap() call itself IIUC. I can change this
test to verify that mremap() call failure then but now the mismatch
of elements between the buffers is what is expected and is happening.

But if you would like I can change the test to check for mremap()
failure in this case (which will fail in the current mainline but
will pass eventually when Mike's patch is in). Please do suggest.