On Wed 09-05-18 14:04:21, Huaisheng HS1 Ye wrote:
> > From: owner-linux-mm(a)kvack.org [mailto:email@example.com] On Behalf Of
> > On Wed 09-05-18 04:22:10, Huaisheng HS1 Ye wrote:
> > > Current mm treats all memory regions equally, it divides zones just by
> > 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
It has advantages but also disadvantages, which need to be clarified and discussed.