On 5 August 2013 13:02, Michal Hocko <mhocko@suse.cz> wrote:

> On Mon 05-08-13 10:10:08, Manjunath Goudar wrote:
> > On 4 August 2013 13:24, Wanpeng Li <liwanp@linux.vnet.ibm.com> wrote:
> >
> > > On Sun, Aug 04, 2013 at 10:41:01AM +0530, Manjunath Goudar wrote:
> > > >s patch adds a Kconfig dependency on an MMU being available before
> > > >CMA can be enabled.  Without this patch, CMA can be enabled on an
> > > >MMU-less system which can lead to issues. This was discovered during
> > > >randconfig testing, in which CMA was enabled w/o MMU being enabled,
> > > >leading to the following error:
> > > >
> > > > CC      mm/migrate.o
> > > >mm/migrate.c: In function ‘remove_migration_pte’:
> > > >mm/migrate.c:134:3: error: implicit declaration of function
> > > ‘pmd_trans_huge’
> > > >[-Werror=implicit-function-declaration]
> > > >   if (pmd_trans_huge(*pmd))
> > > >   ^
> > > >mm/migrate.c:137:3: error: implicit declaration of function
> > > ‘pte_offset_map’
> > > >[-Werror=implicit-function-declaration]
> > > >   ptep = pte_offset_map(pmd, addr);
> > > >
> > >
> > > Similar one.
> > >
> > > http://marc.info/?l=linux-mm&m=137532486405085&w=2
> >
> >
> > In this patch MIGRATION config is not required MMU, because already CMA
> > config depends
> > on MMU and HAVE_MEMBLOCK if both are true then only selecting MIGRATION
> and
> > MEMORY_ISOLATION.
>
> No, I think it should be config MIGRATION that should depend on MMU
> explicitly because that is where the problem exists. It shouldn't rely
> on other configs to not select it automatically.
>
>  Yes you are correct.

The question is. Does CMA need to depend on MMU as well? Why?
> But please comment on the original thread instead.
>

I went through the mm/Kconfig, I think MMU dependence is not required
for CMA.


--
> Michal Hocko
> SUSE Labs
>

Thanks
Manjunath Goudar