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    SubjectRE: [External] [RFC PATCH v1 3/6] mm, zone_type: create ZONE_NVM and fill into GFP_ZONE_TABLE
    Date
    > 
    > On Wed 09-05-18 14:04:21, Huaisheng HS1 Ye wrote:
    > > > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On Behalf Of
    > Michal Hocko
    > > >
    > > > On Wed 09-05-18 04:22:10, Huaisheng HS1 Ye wrote:
    > [...]
    > > > > Current mm treats all memory regions equally, it divides zones just by size,
    > like
    > > > 16M for DMA, 4G for DMA32, and others above for Normal.
    > > > > The spanned range of all zones couldn't be overlapped.
    > > >
    > > > No, this is not correct. Zones can overlap.
    > >
    > > Hi Michal,
    > >
    > > Thanks for pointing it out.
    > > But function zone_sizes_init decides
    > > arch_zone_lowest/highest_possible_pfn's size by max_low_pfn, then
    > > free_area_init_nodes/node are responsible for calculating the spanned
    > > size of zones from memblock memory regions. So, ZONE_DMA and
    > > ZONE_DMA32 and ZONE_NORMAL have separate address scope. How can they
    > > be overlapped with each other?
    >
    > Sorry, I could have been a bit more specific. DMA, DMA32 and Normal
    > zones are exclusive. They are mapped to a specific physical range of
    > memory so they cannot overlap. I was referring to a general property
    > that zones might interleave. Especially zone Normal, Movable and Device.

    Exactly, here ZONE_NVM is a real physical range same as ZONE_DMA, ZONE_DMA32 and ZONE_Normal. So, it couldn't overlap with other zones.
    Just like you mentioned, ZONE_MOVABLE is virtual zone, which comes ZONE_Normal.
    The way of virtual zone is another implementation compared with current patch for ZONE_NVM.
    It has advantages but also disadvantages, which need to be clarified and discussed.

    Sincerely,
    Huaisheng Ye

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