linux-kernel - Re: [PATCH] mm: memcontrol: Use int for event/state parameter in several functions

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Date:   Fri, 28 Jul 2017 11:23:54 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Doug Anderson <dianders@...omium.org>
Subject: Re: [PATCH] mm: memcontrol: Use int for event/state parameter in
 several functions

El Thu, Jul 27, 2017 at 02:10:04PM -0700 Matthias Kaehlcke ha dit:

> Several functions use an enum type as parameter for an event/state,
> but are called in some locations with an argument of a different enum
> type. Adjust the interface of these functions to reality by changing the
> parameter to int.
> 
> This fixes a ton of enum-conversion warnings that are generated when
> building the kernel with clang.

While building for another target with a different configuration I
noticed that inc/dec/mod_memcg_page_state() are also called with a
conflicting enum type. Changing the parameter type for these functions
also would make the API more consistent, with the current patch there
is a somewhat odd mix of related functions, with some receiving an
enum and others an int.

Depending on your preference I can send a v3 of this patch or a
separate patch to address the remaining functions (since this patch
has already been added to -mm).

> ---
>  include/linux/memcontrol.h | 20 ++++++++++++--------
>  mm/memcontrol.c            |  4 +++-
>  2 files changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 3914e3dd6168..80edbc04361e 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -487,8 +487,9 @@ extern int do_swap_account;
>  void lock_page_memcg(struct page *page);
>  void unlock_page_memcg(struct page *page);
>  
> +/* idx can be of type enum memcg_stat_item or node_stat_item */
>  static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
> -					     enum memcg_stat_item idx)
> +					     int idx)
>  {
>  	long val = 0;
>  	int cpu;
> @@ -502,15 +503,17 @@ static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
>  	return val;
>  }
>  
> +/* idx can be of type enum memcg_stat_item or node_stat_item */
>  static inline void __mod_memcg_state(struct mem_cgroup *memcg,
> -				     enum memcg_stat_item idx, int val)
> +				     int idx, int val)
>  {
>  	if (!mem_cgroup_disabled())
>  		__this_cpu_add(memcg->stat->count[idx], val);
>  }
>  
> +/* idx can be of type enum memcg_stat_item or node_stat_item */
>  static inline void mod_memcg_state(struct mem_cgroup *memcg,
> -				   enum memcg_stat_item idx, int val)
> +				   int idx, int val)
>  {
>  	if (!mem_cgroup_disabled())
>  		this_cpu_add(memcg->stat->count[idx], val);
> @@ -631,8 +634,9 @@ static inline void count_memcg_events(struct mem_cgroup *memcg,
>  		this_cpu_add(memcg->stat->events[idx], count);
>  }
>  
> +/* idx can be of type enum memcg_stat_item or node_stat_item */
>  static inline void count_memcg_page_event(struct page *page,
> -					  enum memcg_stat_item idx)
> +					  int idx)
>  {
>  	if (page->mem_cgroup)
>  		count_memcg_events(page->mem_cgroup, idx, 1);
> @@ -840,19 +844,19 @@ static inline bool mem_cgroup_oom_synchronize(bool wait)
>  }
>  
>  static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
> -					     enum memcg_stat_item idx)
> +					     int idx)
>  {
>  	return 0;
>  }
>  
>  static inline void __mod_memcg_state(struct mem_cgroup *memcg,
> -				     enum memcg_stat_item idx,
> +				     int idx,
>  				     int nr)
>  {
>  }
>  
>  static inline void mod_memcg_state(struct mem_cgroup *memcg,
> -				   enum memcg_stat_item idx,
> +				   int idx,
>  				   int nr)
>  {
>  }
> @@ -918,7 +922,7 @@ static inline void count_memcg_events(struct mem_cgroup *memcg,
>  }
>  
>  static inline void count_memcg_page_event(struct page *page,
> -					  enum memcg_stat_item idx)
> +					  int idx)
>  {
>  }
>  
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3df3c04d73ab..460130d2a796 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -550,10 +550,12 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
>   * value, and reading all cpu value can be performance bottleneck in some
>   * common workload, threshold and synchronization as vmstat[] should be
>   * implemented.
> + *
> + * The parameter idx can be of type enum memcg_event_item or vm_event_item.
>   */
>  
>  static unsigned long memcg_sum_events(struct mem_cgroup *memcg,
> -				      enum memcg_event_item event)
> +				      int event)
>  {
>  	unsigned long val = 0;
>  	int cpu;