On Thu, Jan 16, 2020 at 10:23 PM Pingfan Liu <kernelfans@xxxxxxxxx> wrote:
>
> On Thu, Jan 16, 2020 at 3:50 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
> >
> > On Thu 16-01-20 11:01:08, Pingfan Liu wrote:
> > > When fully deactivated, it is meaningless to keep the value of a section's
> > > mem_map. And its mem_map will be reassigned during re-added.
> > >
> > > Beside this, it breaks the user space tool "makedumpfile", which makes
> > > assumption that a hot-removed section having mem_map as NULL.
> >
> > We used to do that before ba72b4c8cf60 ("mm/sparsemem: support
> > sub-section hotplug"). Dan was this an intentional change?
> I do not know the purpose of this. But the change just leave section
> start pfn in fully deactivated section_mem_map, and not used any more.
Not intentional, IIRC at the time I had convinced myself that the
value would always be translated by sparse_decode_mem_map(), so I
thought it could be hiding NULL de-references. I don't see any harm
in the patch.
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