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

[David Hildenbrand <david@redhat.com>]

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


-- 
Thanks,

David / dhildenb