Re: [PATCH] mm/sparse: reset section's mem_map when fully deactivated

[Pingfan Liu <kernelfans@gmail.com>]

On Fri, Jan 17, 2020 at 3:47 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Thu 16-01-20 23:14:02, Dan Williams wrote:
> > On Thu, Jan 16, 2020 at 10:23 PM Pingfan Liu <kernelfans@gmail.com> wrote:
> > >
> > > On Thu, Jan 16, 2020 at 3:50 PM Michal Hocko <mhocko@suse.com> 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.
Should I post V2 with this commit log?

Thanks,
Pingfan