linux-kernel - Re: [PATCH 3/3] memcg: simplify and inline __mem_cgroup_from

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Date:	Fri, 16 Oct 2015 16:17:26 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] memcg: simplify and inline __mem_cgroup_from_kmem

On Mon, Oct 05, 2015 at 01:21:43AM +0300, Vladimir Davydov wrote:
> Before the previous patch, __mem_cgroup_from_kmem had to handle two
> types of kmem - slab pages and pages allocated with alloc_kmem_pages -
> differently, because slab pages did not store information about owner
> memcg in the page struct. Now we can unify it. Since after it, this
> function becomes tiny we can fold it into mem_cgroup_from_kmem.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
> ---
>  include/linux/memcontrol.h |  7 ++++---
>  mm/memcontrol.c            | 18 ------------------
>  2 files changed, 4 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 8a9b7a798f14..0e2e039609d1 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -769,8 +769,6 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg)
>  struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep);
>  void __memcg_kmem_put_cache(struct kmem_cache *cachep);
>  
> -struct mem_cgroup *__mem_cgroup_from_kmem(void *ptr);
> -
>  static inline bool __memcg_kmem_bypass(gfp_t gfp)
>  {
>  	if (!memcg_kmem_enabled())
> @@ -832,9 +830,12 @@ static __always_inline void memcg_kmem_put_cache(struct kmem_cache *cachep)
>  
>  static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
>  {
> +	struct page *page;
> +
>  	if (!memcg_kmem_enabled())
>  		return NULL;
> -	return __mem_cgroup_from_kmem(ptr);
> +	page = virt_to_head_page(ptr);
> +	return page->mem_cgroup;
>  }

virt_to_head_page() is defined in <linux/mm.h> but you don't include it,
and the commit breaks build for me (on v4.3-rc5-mmotm-2015-10-15-15-20).

  CC      arch/x86/kernel/asm-offsets.s
In file included from /home/kas/linux/mm/include/linux/swap.h:8:0,
                 from /home/kas/linux/mm/include/linux/suspend.h:4,
                 from /home/kas/linux/mm/arch/x86/kernel/asm-offsets.c:12:
/home/kas/linux/mm/include/linux/memcontrol.h: In function âmem_cgroup_from_kmemâ:
/home/kas/linux/mm/include/linux/memcontrol.h:841:9: error: implicit declaration of function âvirt_to_head_pageâ [-Werror=implicit-function-declaration]
  page = virt_to_head_page(ptr);
         ^
/home/kas/linux/mm/include/linux/memcontrol.h:841:7: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
  page = virt_to_head_page(ptr);
       ^
In file included from /home/kas/linux/mm/include/linux/suspend.h:8:0,
                 from /home/kas/linux/mm/arch/x86/kernel/asm-offsets.c:12:
/home/kas/linux/mm/include/linux/mm.h: At top level:
/home/kas/linux/mm/include/linux/mm.h:452:28: error: conflicting types for âvirt_to_head_pageâ
 static inline struct page *virt_to_head_page(const void *x)
                            ^
In file included from /home/kas/linux/mm/include/linux/swap.h:8:0,
                 from /home/kas/linux/mm/include/linux/suspend.h:4,
                 from /home/kas/linux/mm/arch/x86/kernel/asm-offsets.c:12:
/home/kas/linux/mm/include/linux/memcontrol.h:841:9: note: previous implicit declaration of âvirt_to_head_pageâ was here
  page = virt_to_head_page(ptr);
         ^
cc1: some warnings being treated as errors

The patch below fixes it for me (and for allmodconfig on x86-64), but I'm not
sure if it have any side effects on other configurations.

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 47677acb4516..e8e52e502c20 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -26,6 +26,7 @@
 #include <linux/page_counter.h>
 #include <linux/vmpressure.h>
 #include <linux/eventfd.h>
+#include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/writeback.h>
 
-- 
 Kirill A. Shutemov
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