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Subject: Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing
 mirroring functionality
References: <1499357846-7481-1-git-send-email-mike.kravetz@oracle.com>
 <1499357846-7481-2-git-send-email-mike.kravetz@oracle.com>
 <ea962c4b-3d47-2a95-7697-2efb4e8cd2f0@linux.vnet.ibm.com>
From: Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <3a43d5fa-223d-1315-513b-85d3a09a07b6@oracle.com>
Date: Fri, 7 Jul 2017 10:14:53 -0700
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To: Anshuman Khandual <khandual@linux.vnet.ibm.com>, linux-mm@kvack.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Michal Hocko <mhocko@suse.com>, Aaron Lu <aaron.lu@intel.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>

On 07/07/2017 01:45 AM, Anshuman Khandual wrote:
> On 07/06/2017 09:47 PM, Mike Kravetz wrote:
>> The mremap system call has the ability to 'mirror' parts of an existing
>> mapping.  To do so, it creates a new mapping that maps the same pages as
>> the original mapping, just at a different virtual address.  This
>> functionality has existed since at least the 2.6 kernel.
>>
>> This patch simply adds a new flag to mremap which will make this
>> functionality part of the API.  It maintains backward compatibility with
>> the existing way of requesting mirroring (old_size == 0).
>>
>> If this new MREMAP_MIRROR flag is specified, then new_size must equal
>> old_size.  In addition, the MREMAP_MAYMOVE flag must be specified.
> 
> Yeah it all looks good. But why is this requirement that if
> MREMAP_MAYMOVE is specified then old_size and new_size must
> be equal.

No real reason.  I just wanted to clearly separate the new interface from
the old.  On second thought, it would be better to require old_size == 0
as in the legacy interface.

-- 
Mike Kravetz

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