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

From: Hugh Dickins
Date: Fri Oct 16 2015 - 18:12:41 EST

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@xxxxxxxxxxxxx>
> > > ---
> > > 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)
{