linux-kernel - RE: [External] [RFC PATCH v1 3/6] mm, zone_type: create ZONE_NVM and fill into GFP_ZONE

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Date:   Thu, 10 May 2018 03:53:34 +0000
From:   Huaisheng HS1 Ye <yehs1@...ovo.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Randy Dunlap <rdunlap@...radead.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "willy@...radead.org" <willy@...radead.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "pasha.tatashin@...cle.com" <pasha.tatashin@...cle.com>,
        "alexander.levin@...izon.com" <alexander.levin@...izon.com>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "penguin-kernel@...ove.SAKURA.ne.jp" 
        <penguin-kernel@...ove.SAKURA.ne.jp>,
        "colyli@...e.de" <colyli@...e.de>,
        NingTing Cheng <chengnt@...ovo.com>,
        "Ocean HY1 He" <hehy1@...ovo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: RE: [External] [RFC PATCH v1 3/6] mm, zone_type: create ZONE_NVM and
 fill into GFP_ZONE_TABLE

> 
> On Wed 09-05-18 14:04:21, Huaisheng HS1 Ye wrote:
> > > From: owner-linux-mm@...ck.org [mailto:owner-linux-mm@...ck.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