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Date:   Wed, 10 Mar 2021 11:30:50 -0800
From:   Roman Gushchin <guro@fb.com>
To:     Muchun Song <songmuchun@bytedance.com>
CC:     <hannes@cmpxchg.org>, <mhocko@kernel.org>,
        <akpm@linux-foundation.org>, <shakeelb@google.com>,
        <vdavydov.dev@gmail.com>, <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH v3 4/4] mm: memcontrol: move PageMemcgKmem to the scope
 of CONFIG_MEMCG_KMEM
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On Tue, Mar 09, 2021 at 06:07:17PM +0800, Muchun Song wrote:
> The page only can be marked as kmem when CONFIG_MEMCG_KMEM is enabled.
> So move PageMemcgKmem() to the scope of the CONFIG_MEMCG_KMEM.
> 
> As a bonus, on !CONFIG_MEMCG_KMEM build some code can be compiled out.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Nice!

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!

> ---
>  include/linux/memcontrol.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 07c449af9c0f..d3ca8c8e7fc3 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -469,6 +469,7 @@ static inline struct mem_cgroup *page_memcg_check(struct page *page)
>  	return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
>  }
>  
> +#ifdef CONFIG_MEMCG_KMEM
>  /*
>   * PageMemcgKmem - check if the page has MemcgKmem flag set
>   * @page: a pointer to the page struct
> @@ -483,7 +484,6 @@ static inline bool PageMemcgKmem(struct page *page)
>  	return page->memcg_data & MEMCG_DATA_KMEM;
>  }
>  
> -#ifdef CONFIG_MEMCG_KMEM
>  /*
>   * page_objcgs - get the object cgroups vector associated with a page
>   * @page: a pointer to the page struct
> @@ -544,6 +544,11 @@ static inline struct obj_cgroup *page_objcg(struct page *page)
>  	return (struct obj_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK);
>  }
>  #else
> +static inline bool PageMemcgKmem(struct page *page)
> +{
> +	return false;
> +}
> +
>  static inline struct obj_cgroup **page_objcgs(struct page *page)
>  {
>  	return NULL;
> -- 
> 2.11.0
>