Re: [PATCH 3/3] memcg: simplify and inline __mem_cgroup_from_kmem

[Hugh Dickins <hughd@google.com>]

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On Fri, 16 Oct 2015, Vladimir Davydov wrote:
> On Fri, Oct 16, 2015 at 04:17:26PM +0300, Kirill A. Shutemov wrote:
> > 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@virtuozzo.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 â?~mem_cgroup_from_kmemâ?T:
> > /home/kas/linux/mm/include/linux/memcontrol.h:841:9: error: implicit declaration of function â?~virt_to_head_pageâ?T [-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 â?~virt_to_head_pageâ?T
> >  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 â?~virt_to_head_pageâ?T was here
> >   page = virt_to_head_page(ptr);
> >          ^
> > cc1: some warnings being treated as errors
> 
> Oops, in my config I have CONFIG_CGROUP_WRITEBACK enabled, which results
> in including mm.h to memcontrol.h indirectly:
> 
>  linux/memcontrol.h
>   linux/writeback.h
>    linux/bio.h
>     linux/highmem.h
>      linux/mm.h
> 
> That's why I didn't notice this. Sorry about that.
> 
> > 
> > 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.
> 
> It should work OK with any config, otherwise CONFIG_CGROUP_WRITEBACK
> would be broken too.
> 
> Andrew, could you please merge the fix by Kirill into
> memcg-simplify-and-inline-__mem_cgroup_from_kmem.patch
> 
> Thanks,
> Vladimir
> 
> > 
> > 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>
> >  

Are you expecting to use mem_cgroup_from_kmem() from other places
in future?  Seems possible; but at present it's called from only
one place, and (given how memcontrol.h has somehow managed to avoid
including mm.h all these years), I thought it would be nice to avoid
it for just this; and fixed my build with the patch below last night.
Whatever you all think best: just wanted to point out an alternative.

Hugh

--- 4035m/include/linux/memcontrol.h	2015-10-15 15:26:59.503568644 -0700
+++ 4035M/include/linux/memcontrol.h	2015-10-16 03:09:10.000000000 -0700
@@ -831,16 +831,6 @@ static __always_inline void memcg_kmem_p
 	if (memcg_kmem_enabled())
 		__memcg_kmem_put_cache(cachep);
 }
-
-static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
-	struct page *page;
-
-	if (!memcg_kmem_enabled())
-		return NULL;
-	page = virt_to_head_page(ptr);
-	return page->mem_cgroup;
-}
 #else
 #define for_each_memcg_cache_index(_idx)	\
 	for (; NULL; )
@@ -886,11 +876,5 @@ memcg_kmem_get_cache(struct kmem_cache *
 static inline void memcg_kmem_put_cache(struct kmem_cache *cachep)
 {
 }
-
-static inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
-{
-	return NULL;
-}
 #endif /* CONFIG_MEMCG_KMEM */
 #endif /* _LINUX_MEMCONTROL_H */
-
--- 4035m/mm/list_lru.c	2015-10-15 15:26:59.835572128 -0700
+++ 4035M/mm/list_lru.c	2015-10-16 03:11:51.000000000 -0700
@@ -63,6 +63,16 @@ list_lru_from_memcg_idx(struct list_lru_
 	return &nlru->lru;
 }
 
+static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr)
+{
+	struct page *page;
+
+	if (!memcg_kmem_enabled())
+		return NULL;
+	page = virt_to_head_page(ptr);
+	return page->mem_cgroup;
+}
+
 static inline struct list_lru_one *
 list_lru_from_kmem(struct list_lru_node *nlru, void *ptr)
 {