On Thu 16-01-20 23:14:02, Dan Williams wrote:
> 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.
Thanks for the confirmation. It would be great to have this in the
changelog.
--
Michal Hocko
SUSE Labs
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