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Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality

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On 07/07/2017 10:44 PM, Mike Kravetz wrote:
> 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.

That would be redundant. Mirroring will just happen because old_size is
0 whether we mention the MREMAP_MIRROR flag or not. IMHO it should just
mirror if the flag is specified irrespective of the old_size value.

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[RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-06 18:20 +0200
  Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-07-07 10:50 +0200
    Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-07 19:20 +0200
      Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-07-09 09:30 +0200
  Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-07-07 12:30 +0200
    Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-07 19:40 +0200
      Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-07-07 19:50 +0200
        Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-07 20:20 +0200
          Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-07-09 09:40 +0200
            Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Vlastimil Babka <vbabka@suse.cz> - 2017-07-10 18:30 +0200
              Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-10 19:30 +0200
  Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Michal Hocko <mhocko@kernel.org> - 2017-07-11 14:40 +0200
    Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-11 20:30 +0200
      Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Andrea Arcangeli <aarcange@redhat.com> - 2017-07-11 23:10 +0200
        Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-12 00:00 +0200
          Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Andrea Arcangeli <aarcange@redhat.com> - 2017-07-12 01:40 +0200
      Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Michal Hocko <mhocko@kernel.org> - 2017-07-12 13:50 +0200
        Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-12 19:00 +0200
          Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Michal Hocko <mhocko@kernel.org> - 2017-07-13 08:20 +0200
            Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-13 18:10 +0200
              Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Andrea Arcangeli <aarcange@redhat.com> - 2017-07-13 18:40 +0200
                Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Mike Kravetz <mike.kravetz@oracle.com> - 2017-07-13 20:20 +0200
                Re: [RFC PATCH 1/1] mm/mremap: add MREMAP_MIRROR flag for existing  mirroring functionality Andrea Arcangeli <aarcange@redhat.com> - 2017-07-13 22:40 +0200

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