Re: [PATCH] mm, memcg: fix build error around the usage of kmem_caches

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Feb 6, 2020 at 1:19 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 05.02.20 18:03, Yafang Shao wrote:
> > When I manually set default n to MEMCG_KMEM in init/Kconfig, bellow error
> > occurs,
> >
> > mm/slab_common.c: In function 'memcg_slab_start':
> > mm/slab_common.c:1530:30: error: 'struct mem_cgroup' has no member named
> > 'kmem_caches'
> >   return seq_list_start(&memcg->kmem_caches, *pos);
> >                               ^
> > mm/slab_common.c: In function 'memcg_slab_next':
> > mm/slab_common.c:1537:32: error: 'struct mem_cgroup' has no member named
> > 'kmem_caches'
> >   return seq_list_next(p, &memcg->kmem_caches, pos);
> >                                 ^
> > mm/slab_common.c: In function 'memcg_slab_show':
> > mm/slab_common.c:1551:16: error: 'struct mem_cgroup' has no member named
> > 'kmem_caches'
> >   if (p == memcg->kmem_caches.next)
> >                 ^
> >   CC      arch/x86/xen/smp.o
> > mm/slab_common.c: In function 'memcg_slab_start':
> > mm/slab_common.c:1531:1: warning: control reaches end of non-void function
> > [-Wreturn-type]
> >  }
> >  ^
> > mm/slab_common.c: In function 'memcg_slab_next':
> > mm/slab_common.c:1538:1: warning: control reaches end of non-void function
> > [-Wreturn-type]
> >  }
> >  ^
> >
> > That's because kmem_caches is defined only when CONFIG_MEMCG_KMEM is set,
> > while memcg_slab_start() will use it no matter CONFIG_MEMCG_KMEM is defined
> > or not.
> >
> > By the way, the reason I mannuly undefined CONFIG_MEMCG_KMEM is to verify
> > whether my some other code change is still stable when CONFIG_MEMCG_KMEM is
> > not set. Unfortunately, the existing code has been already unstable since
> > v4.11.
> >
> > Fixes: bc2791f857e1 ("slab: link memcg kmem_caches on their associated memory cgroup")
> > Cc: Tejun Heo <tj@kernel.org>
> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  mm/memcontrol.c  | 2 ++
> >  mm/slab_common.c | 2 +-
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 6f6dc8712e39..43f0125b45bb 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -4723,6 +4723,7 @@ static struct cftype mem_cgroup_legacy_files[] = {
> >               .write = mem_cgroup_reset,
> >               .read_u64 = mem_cgroup_read_u64,
> >       },
> > +#ifdef CONFIG_MEMCG_KMEM
> >  #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
>
> Not sure if
>
> #if defined(CONFIG_MEMCG_KMEM) && \
>     (defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG))
>
> is preffered
>

Seems better. Thanks for your suggestion.

Thanks
Yafang