Re: [PATCH] MM: Make Contiguous Memory Allocator depends on MMU

[Michal Hocko <mhocko@suse.cz>]

On Mon 05-08-13 14:07:41, Manjunath Goudar wrote:
> 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 a??remove_migration_ptea??:
> > > > >mm/migrate.c:134:3: error: implicit declaration of function
> > > > a??pmd_trans_hugea??
> > > > >[-Werror=implicit-function-declaration]
> > > > >   if (pmd_trans_huge(*pmd))
> > > > >   ^
> > > > >mm/migrate.c:137:3: error: implicit declaration of function
> > > > a??pte_offset_mapa??
> > > > >[-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.

OK, it turned out that it is needed in the end. Kcofing forces selects
so CMA config would force MIGRATION even if that one depends on MMU.

-- 
Michal Hocko
SUSE Labs

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