RE: [PATCH v1] mm: Defines obj_cgroup_get() if CONFIG_MEMCG is not defined.

["Sridhar, Kanchana P" <kanchana.p.sridhar@intel.com>]

Hi Michal,

> -----Original Message-----
> From: Michal Hocko <mhocko@suse.com>
> Sent: Wednesday, August 21, 2024 8:11 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@intel.com>
> Cc: linux-kernel@vger.kernel.org; linux-mm@kvack.org;
> hannes@cmpxchg.org; yosryahmed@google.com; nphamcs@gmail.com;
> ryan.roberts@arm.com; Huang, Ying <ying.huang@intel.com>;
> 21cnbao@gmail.com; akpm@linux-foundation.org; Zou, Nanhai
> <nanhai.zou@intel.com>; Feghali, Wajdi K <wajdi.k.feghali@intel.com>;
> Gopal, Vinodh <vinodh.gopal@intel.com>
> Subject: Re: [PATCH v1] mm: Defines obj_cgroup_get() if CONFIG_MEMCG is
> not defined.
> 
> On Tue 20-08-24 12:50:05, Kanchana P Sridhar wrote:
> > This resolves an issue with obj_cgroup_get() not being defined
> > if CONFIG_MEMCG is not defined.
> 
> Could you paste the compilation error and which tree this is based on?

Sure, this link contains the compilation error reported by the kernel test robot:

https://lore.kernel.org/oe-kbuild-all/202408202320.trSaY2o4-lkp@intel.com/

Error:
kernel test robot noticed the following build errors:

[auto build test ERROR on 8c0b4f7b65fd1ca7af01267f491e815a40d77444]

url:    https://github.com/intel-lab-lkp/linux/commits/Kanchana-P-Sridhar/mm-zswap-zswap_is_folio_same_filled-takes-an-index-in-the-folio/20240819-101738
base:   8c0b4f7b65fd1ca7af01267f491e815a40d77444
patch link:    https://lore.kernel.org/r/20240819021621.29125-3-kanchana.p.sridhar%40intel.com
patch subject: [PATCH v4 2/4] mm: zswap: zswap_store() extended to handle mTHP folios.
config: sparc-randconfig-002-20240820 (https://download.01.org/0day-ci/archive/20240820/202408202320.trSaY2o4-lkp@intel.com/config)
compiler: sparc-linux-gcc (GCC) 14.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240820/202408202320.trSaY2o4-lkp@intel.com/reproduce)

All errors (new ones prefixed by >>):

   mm/zswap.c: In function 'zswap_store_page':
>> mm/zswap.c:1534:17: error: implicit declaration of function 'obj_cgroup_get'; did you mean 'obj_cgroup_put'? [-Wimplicit-function-declaration]
    1534 |                 obj_cgroup_get(objcg);
         |                 ^~~~~~~~~~~~~~
         |                 obj_cgroup_put

My patch fixing the error is based on the mm-unstable branch in this git tree:

https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/

Please let me know if you need any other info.

Thanks,
Kanchana

> 
> > This causes build errors if
> > obj_cgroup_get() is called from code that is agnostic of CONFIG_MEMCG.
> >
> > The patch resolves this.
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
> > ---
> >  include/linux/memcontrol.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index fe05fdb92779..f693d254ab2a 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -1281,6 +1281,10 @@ struct mem_cgroup
> *mem_cgroup_from_css(struct cgroup_subsys_state *css)
> >  	return NULL;
> >  }
> >
> > +static inline void obj_cgroup_get(struct obj_cgroup *objcg)
> > +{
> > +}
> > +
> >  static inline void obj_cgroup_put(struct obj_cgroup *objcg)
> >  {
> >  }
> >
> > base-commit: 7d0b0d4b77b368b2111fc8b4449e33dfb3c34087
> > --
> > 2.27.0
> >
> 
> --
> Michal Hocko
> SUSE Labs