Re: [akpm-mm:mm-unstable 199/420] mm/memcontrol-v1.c:651:24: error: call to undeclared function 'swp_cluster_offset'; ISO C99 and later do not support implicit function declarations

[Kairui Song <ryncsn@gmail.com>]

On Thu, May 28, 2026 at 02:45:02PM +0800, Andrew Morton wrote:
> On Thu, 28 May 2026 17:58:34 +0800 kernel test robot <lkp@intel.com> wrote:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> > head:   8a74e22643189e0ae339afc91110ddb4cab1941b
> > commit: 93680c2b51fa1f84fe50800b71140dbd283372b8 [199/420] mm/memcg, swap: store cgroup id in cluster table directly
> > config: arm-randconfig-004-20260528 (https://download.01.org/0day-ci/archive/20260528/202605281711.bSeZlErK-lkp@intel.com/config)
> > compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 9409c07de6378507397ecdb6f05f628f58110112)
> > rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260528/202605281711.bSeZlErK-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202605281711.bSeZlErK-lkp@intel.com/
> > 
> > All errors (new ones prefixed by >>):
> > 
> > >> mm/memcontrol-v1.c:651:24: error: call to undeclared function 'swp_cluster_offset'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >      651 |         __swap_cgroup_set(ci, swp_cluster_offset(folio->swap), nr_entries,
> >          |                               ^
> >    mm/memcontrol-v1.c:721:31: error: call to undeclared function 'swp_cluster_offset'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
> >      721 |         id = __swap_cgroup_clear(ci, swp_cluster_offset(folio->swap),
> >          |                                      ^
> >    2 errors generated.
> 
> OK, CONFIG_SWAP=n.

I though we have already fixed this, and this is trigger by the bot
just because its not a squashed commit, so building while iterating
the commit will still fail? Or maybe I have some misunderstanding
here..

https://lore.kernel.org/linux-mm/20260519152620.b7b5fd2d68d635ec8d34ad2c@linux-foundation.org/

> 
> We could hack in a stub for swp_cluster_offset(), but why are we
> compiling __memcg1_swapout() at all when CONFIG_SWAP=n?  Ditto
> memcg1_swapin().
> 
> How does the below look?
> 
> Really this should be done as a preparatory thing, but we'll survive.
> 
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: memcgv1: don't compile swap functions when CONFIG_SWAP=n
> Date: Thu May 28 02:35:22 PM PDT 2026
> 
> Stub these out to save some dead code and to fix a build error with the
> upcoming "mm/memcg, swap: store cgroup id in cluster table directly".
> 
> Link: https://lore.kernel.org/202605281711.bSeZlErK-lkp@intel.com
> Cc: David Hildenbrand <david@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Kairui Song <kasong@tencent.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Muchun Song <muchun.song@linux.dev>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Shakeel Butt <shakeel.butt@linux.dev>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  include/linux/memcontrol.h |   15 ++++++++++-----
>  mm/memcontrol-v1.c         |    2 ++
>  2 files changed, 12 insertions(+), 5 deletions(-)
> 
> --- a/include/linux/memcontrol.h~mm-memcg-swap-store-cgroup-id-in-cluster-table-directly-fix
> +++ a/include/linux/memcontrol.h
> @@ -1900,9 +1900,6 @@ static inline void mem_cgroup_exit_user_
>  	current->in_user_fault = 0;
>  }
>  
> -void __memcg1_swapout(struct folio *folio, struct swap_cluster_info *ci);
> -void memcg1_swapin(struct folio *folio);
> -
>  #else /* CONFIG_MEMCG_V1 */
>  static inline
>  unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
> @@ -1930,6 +1927,15 @@ static inline void mem_cgroup_exit_user_
>  {
>  }
>  
> +#endif /* CONFIG_MEMCG_V1 */
> +
> +#if defined(CONFIG_MEMCG_V1) && defined(CONFIG_SWAP)
> +
> +void __memcg1_swapout(struct folio *folio, struct swap_cluster_info *ci);
> +void memcg1_swapin(struct folio *folio);
> +
> +#else
> +
>  static inline void __memcg1_swapout(struct folio *folio,
>  		struct swap_cluster_info *ci)
>  {
> @@ -1938,7 +1944,6 @@ static inline void __memcg1_swapout(stru
>  static inline void memcg1_swapin(struct folio *folio)
>  {
>  }
> -
> -#endif /* CONFIG_MEMCG_V1 */
> +#endif
>  
>  #endif /* _LINUX_MEMCONTROL_H */
> --- a/mm/memcontrol-v1.c~mm-memcg-swap-store-cgroup-id-in-cluster-table-directly-fix
> +++ a/mm/memcontrol-v1.c
> @@ -604,6 +604,7 @@ void memcg1_commit_charge(struct folio *
>  	local_irq_restore(flags);
>  }
>  
> +#ifdef CONFIG_SWAP
>  /**
>   * __memcg1_swapout - transfer a memsw charge to swap
>   * @folio: folio whose memsw charge to transfer
> @@ -723,6 +724,7 @@ void memcg1_swapin(struct folio *folio)
>  	swap_cluster_unlock(ci);
>  	mem_cgroup_uncharge_swap(id, nr_pages);
>  }
> +#endif
>  
>  void memcg1_uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,
>  			   unsigned long nr_memory, int nid)
> _
> 

Thanks again, looks good to me, the simple is simple and it looks the
same thing I posted previously:
https://lore.kernel.org/linux-mm/ag0mdxBWcrZ8hxPP@KASONG-MC4/