Re: [External] Re: [PATCH v18 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c

[Muchun Song]

On Thu, Mar 11, 2021 at 4:53 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Thu 11-03-21 16:45:51, Muchun Song wrote:
> > On Thu, Mar 11, 2021 at 10:58 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
> > >
> > > On Wed, Mar 10, 2021 at 10:14 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
> > > >
> > > > [I am sorry for a late review]
> > >
> > > Thanks for your review.
> > >
> > > >
> > > > On Mon 08-03-21 18:27:59, Muchun Song wrote:
> > > > > Move bootmem info registration common API to individual bootmem_info.c.
> > > > > And we will use {get,put}_page_bootmem() to initialize the page for the
> > > > > vmemmap pages or free the vmemmap pages to buddy in the later patch.
> > > > > So move them out of CONFIG_MEMORY_HOTPLUG_SPARSE. This is just code
> > > > > movement without any functional change.
> > > > >
> > > > > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > > > > Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > > > > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> > > > > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> > > > > Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> > > > > Tested-by: Chen Huang <chenhuang5@xxxxxxxxxx>
> > > > > Tested-by: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx>
> > > >
> > > > Separation from memory_hotplug.c is definitely a right step. I am
> > > > wondering about the config dependency though
> > > > [...]
> > > > > diff --git a/mm/Makefile b/mm/Makefile
> > > > > index 72227b24a616..daabf86d7da8 100644
> > > > > --- a/mm/Makefile
> > > > > +++ b/mm/Makefile
> > > > > @@ -83,6 +83,7 @@ obj-$(CONFIG_SLUB) += slub.o
> > > > >  obj-$(CONFIG_KASAN)  += kasan/
> > > > >  obj-$(CONFIG_KFENCE) += kfence/
> > > > >  obj-$(CONFIG_FAILSLAB) += failslab.o
> > > > > +obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
> > > >
> > > > I would have expected this would depend on CONFIG_SPARSE.
> > > > BOOTMEM_INFO_NODE is really an odd thing to depend on here. There is
> > > > some functionality which requires the node info but that can be gated
> > > > specifically. Or what is the thinking behind?
> >
> > I have tried this. And I find that it is better to depend on
> > BOOTMEM_INFO_NODE instead of SPARSEMEM.
> >
> > If we enable SPARSEMEM but disable HAVE_BOOTMEM_INFO_NODE,
> > the bootmem_info.c also is compiled. Actually, we do not
> > need those functions on other architectures. And these
> > functions are also related to bootmem info. So it may be
> > more reasonable to depend on BOOTMEM_INFO_NODE.
> > Just my thoughts.
>
> If BOOTMEM_INFO_NODE is disbabled then bootmem_info.c would be
> effectivelly only {get,put}_page_bootmem, no?

{get,put}_page_bootmem also would be effective. I found that
get_page_bootmem is only used in the scope of the
CONFIG_BOOTMEM_INFO_NODE. So I move them
to the bootmem_info.c.

Thanks.

>
> --
> Michal Hocko
> SUSE Labs