[PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Roman Gushchin]

Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
the space for task stacks can be allocated using __vmalloc_node_range(),
alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
second cases page->mem_cgroup pointer is set, but in the third it's
not: memcg membership of a slab page should be determined using the
memcg_from_slab_page() function, which looks at
page->slab_cache->memcg_params.memcg . In this case, using
mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
page->mem_cgroup pointer is NULL even for pages charged to a non-root
memory cgroup.

It can lead to kernel_stack per-memcg counters permanently showing 0
on some architectures (depending on the configuration).

In order to fix it, let's introduce a mod_memcg_obj_state() helper,
which takes a pointer to a kernel object as a first argument, uses
mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
calls mod_memcg_state(). It allows to handle all possible
configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
values) without spilling any memcg/kmem specifics into fork.c .

Note: this patch has been first posted as a part of the new slab
controller patchset. This is a slightly updated version: the fixes
tag has been added and the commit log was extended by the advice
of Johannes Weiner. Because it's a fix that makes sense by itself,
I'm re-posting it as a standalone patch.

Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: stable@vger.kernel.org
---
 include/linux/memcontrol.h |  5 +++++
 kernel/fork.c              |  4 ++--
 mm/memcontrol.c            | 11 +++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3253d5de8243..817ea1d93e0e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -695,6 +695,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 			int val);
 void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val);
+void mod_memcg_obj_state(void *p, int idx, int val);
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
 				    enum node_stat_item idx, int val)
@@ -1129,6 +1130,10 @@ static inline void __mod_lruvec_slab_state(void *p, enum node_stat_item idx,
 	__mod_node_page_state(page_pgdat(page), idx, val);
 }
 
+static inline void mod_memcg_obj_state(void *p, int idx, int val)
+{
+}
+
 static inline
 unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 					    gfp_t gfp_mask,
diff --git a/kernel/fork.c b/kernel/fork.c
index a1f2f5205a61..bdc5004effa4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -404,8 +404,8 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
 		mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
 				    THREAD_SIZE / 1024 * account);
 
-		mod_memcg_page_state(first_page, MEMCG_KERNEL_STACK_KB,
-				     account * (THREAD_SIZE / 1024));
+		mod_memcg_obj_state(stack, MEMCG_KERNEL_STACK_KB,
+				    account * (THREAD_SIZE / 1024));
 	}
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d1ae46838af1..6514df549433 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -776,6 +776,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
 	rcu_read_unlock();
 }
 
+void mod_memcg_obj_state(void *p, int idx, int val)
+{
+	struct mem_cgroup *memcg;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_obj(p);
+	if (memcg)
+		mod_memcg_state(memcg, idx, val);
+	rcu_read_unlock();
+}
+
 /**
  * __count_memcg_events - account VM events in a cgroup
  * @memcg: the memory cgroup
-- 
2.24.1

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Shakeel Butt]

On Tue, Mar 3, 2020 at 3:36 PM Roman Gushchin <guro@fb.com> wrote:
>
> Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> the space for task stacks can be allocated using __vmalloc_node_range(),
> alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> second cases page->mem_cgroup pointer is set, but in the third it's
> not: memcg membership of a slab page should be determined using the
> memcg_from_slab_page() function, which looks at
> page->slab_cache->memcg_params.memcg . In this case, using
> mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> page->mem_cgroup pointer is NULL even for pages charged to a non-root
> memory cgroup.
>
> It can lead to kernel_stack per-memcg counters permanently showing 0
> on some architectures (depending on the configuration).
>
> In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> which takes a pointer to a kernel object as a first argument, uses
> mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> calls mod_memcg_state(). It allows to handle all possible
> configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> values) without spilling any memcg/kmem specifics into fork.c .
>
> Note: this patch has been first posted as a part of the new slab
> controller patchset. This is a slightly updated version: the fixes
> tag has been added and the commit log was extended by the advice
> of Johannes Weiner. Because it's a fix that makes sense by itself,
> I'm re-posting it as a standalone patch.
>
> Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
> Signed-off-by: Roman Gushchin <guro@fb.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Johannes Weiner]

On Tue, Mar 03, 2020 at 03:35:50PM -0800, Roman Gushchin wrote:
> Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> the space for task stacks can be allocated using __vmalloc_node_range(),
> alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> second cases page->mem_cgroup pointer is set, but in the third it's
> not: memcg membership of a slab page should be determined using the
> memcg_from_slab_page() function, which looks at
> page->slab_cache->memcg_params.memcg . In this case, using
> mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> page->mem_cgroup pointer is NULL even for pages charged to a non-root
> memory cgroup.
> 
> It can lead to kernel_stack per-memcg counters permanently showing 0
> on some architectures (depending on the configuration).
> 
> In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> which takes a pointer to a kernel object as a first argument, uses
> mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> calls mod_memcg_state(). It allows to handle all possible
> configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> values) without spilling any memcg/kmem specifics into fork.c .
> 
> Note: this patch has been first posted as a part of the new slab
> controller patchset. This is a slightly updated version: the fixes
> tag has been added and the commit log was extended by the advice
> of Johannes Weiner. Because it's a fix that makes sense by itself,
> I'm re-posting it as a standalone patch.
> 
> Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: stable@vger.kernel.org

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Thanks for pointing out the user impact.

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Andrew Morton]

On Tue, 3 Mar 2020 15:35:50 -0800 Roman Gushchin <guro@fb.com> wrote:

> Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> the space for task stacks can be allocated using __vmalloc_node_range(),
> alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> second cases page->mem_cgroup pointer is set, but in the third it's
> not: memcg membership of a slab page should be determined using the
> memcg_from_slab_page() function, which looks at
> page->slab_cache->memcg_params.memcg . In this case, using
> mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> page->mem_cgroup pointer is NULL even for pages charged to a non-root
> memory cgroup.
> 
> It can lead to kernel_stack per-memcg counters permanently showing 0
> on some architectures (depending on the configuration).
> 
> In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> which takes a pointer to a kernel object as a first argument, uses
> mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> calls mod_memcg_state(). It allows to handle all possible
> configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> values) without spilling any memcg/kmem specifics into fork.c .
> 
> Note: this patch has been first posted as a part of the new slab
> controller patchset. This is a slightly updated version: the fixes
> tag has been added and the commit log was extended by the advice
> of Johannes Weiner. Because it's a fix that makes sense by itself,
> I'm re-posting it as a standalone patch.

Actually, it isn't a standalone patch.

> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -776,6 +776,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
>  	rcu_read_unlock();
>  }
>  
> +void mod_memcg_obj_state(void *p, int idx, int val)
> +{
> +	struct mem_cgroup *memcg;
> +
> +	rcu_read_lock();
> +	memcg = mem_cgroup_from_obj(p);
> +	if (memcg)
> +		mod_memcg_state(memcg, idx, val);
> +	rcu_read_unlock();
> +}

mem_cgroup_from_obj() is later added by
http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com

We could merge both mm-memcg-slab-introduce-mem_cgroup_from_obj.patch
and this patch, but that's a whole lot of stuff to backport into
-stable.

Are you able to come up with a simpler suitable-for-stable fix?

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Roman Gushchin]

On Sat, Mar 21, 2020 at 04:48:56PM -0700, Andrew Morton wrote:
> On Tue, 3 Mar 2020 15:35:50 -0800 Roman Gushchin <guro@fb.com> wrote:
> 
> > Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> > the space for task stacks can be allocated using __vmalloc_node_range(),
> > alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> > second cases page->mem_cgroup pointer is set, but in the third it's
> > not: memcg membership of a slab page should be determined using the
> > memcg_from_slab_page() function, which looks at
> > page->slab_cache->memcg_params.memcg . In this case, using
> > mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> > page->mem_cgroup pointer is NULL even for pages charged to a non-root
> > memory cgroup.
> > 
> > It can lead to kernel_stack per-memcg counters permanently showing 0
> > on some architectures (depending on the configuration).
> > 
> > In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> > which takes a pointer to a kernel object as a first argument, uses
> > mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> > calls mod_memcg_state(). It allows to handle all possible
> > configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> > values) without spilling any memcg/kmem specifics into fork.c .
> > 
> > Note: this patch has been first posted as a part of the new slab
> > controller patchset. This is a slightly updated version: the fixes
> > tag has been added and the commit log was extended by the advice
> > of Johannes Weiner. Because it's a fix that makes sense by itself,
> > I'm re-posting it as a standalone patch.
> 
> Actually, it isn't a standalone patch.

It's true. I only meant it doesn't have to be a part of the slab accounting
rework patchset.

> 
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -776,6 +776,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
> >  	rcu_read_unlock();
> >  }
> >  
> > +void mod_memcg_obj_state(void *p, int idx, int val)
> > +{
> > +	struct mem_cgroup *memcg;
> > +
> > +	rcu_read_lock();
> > +	memcg = mem_cgroup_from_obj(p);
> > +	if (memcg)
> > +		mod_memcg_state(memcg, idx, val);
> > +	rcu_read_unlock();
> > +}
> 
> mem_cgroup_from_obj() is later added by
> http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com
> 
> We could merge both mm-memcg-slab-introduce-mem_cgroup_from_obj.patch
> and this patch, but that's a whole lot of stuff to backport into
> -stable.
> 
> Are you able to come up with a simpler suitable-for-stable fix?

I'll try.

Thank you!

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Roman Gushchin]

On Sat, Mar 21, 2020 at 04:48:56PM -0700, Andrew Morton wrote:
> On Tue, 3 Mar 2020 15:35:50 -0800 Roman Gushchin <guro@fb.com> wrote:
> 
> > Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio
> > the space for task stacks can be allocated using __vmalloc_node_range(),
> > alloc_pages_node() and kmem_cache_alloc_node(). In the first and the
> > second cases page->mem_cgroup pointer is set, but in the third it's
> > not: memcg membership of a slab page should be determined using the
> > memcg_from_slab_page() function, which looks at
> > page->slab_cache->memcg_params.memcg . In this case, using
> > mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
> > page->mem_cgroup pointer is NULL even for pages charged to a non-root
> > memory cgroup.
> > 
> > It can lead to kernel_stack per-memcg counters permanently showing 0
> > on some architectures (depending on the configuration).
> > 
> > In order to fix it, let's introduce a mod_memcg_obj_state() helper,
> > which takes a pointer to a kernel object as a first argument, uses
> > mem_cgroup_from_obj() to get a RCU-protected memcg pointer and
> > calls mod_memcg_state(). It allows to handle all possible
> > configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE
> > values) without spilling any memcg/kmem specifics into fork.c .
> > 
> > Note: this patch has been first posted as a part of the new slab
> > controller patchset. This is a slightly updated version: the fixes
> > tag has been added and the commit log was extended by the advice
> > of Johannes Weiner. Because it's a fix that makes sense by itself,
> > I'm re-posting it as a standalone patch.
> 
> Actually, it isn't a standalone patch.
> 
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -776,6 +776,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
> >  	rcu_read_unlock();
> >  }
> >  
> > +void mod_memcg_obj_state(void *p, int idx, int val)
> > +{
> > +	struct mem_cgroup *memcg;
> > +
> > +	rcu_read_lock();
> > +	memcg = mem_cgroup_from_obj(p);
> > +	if (memcg)
> > +		mod_memcg_state(memcg, idx, val);
> > +	rcu_read_unlock();
> > +}
> 
> mem_cgroup_from_obj() is later added by
> http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com
> 
> We could merge both mm-memcg-slab-introduce-mem_cgroup_from_obj.patch
> and this patch, but that's a whole lot of stuff to backport into
> -stable.
> 
> Are you able to come up with a simpler suitable-for-stable fix?

How about this one? I've merged them into one and stripped it a little bit.

Thanks!

--

From 1b8b039b05d49945aaf34a0600b04ea616fe0ba2 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Sat, 21 Mar 2020 23:05:42 +0000
Subject: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack
 implementations

Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio the
space for task stacks can be allocated using __vmalloc_node_range(),
alloc_pages_node() and kmem_cache_alloc_node().  In the first and the
second cases page->mem_cgroup pointer is set, but in the third it's not:
memcg membership of a slab page should be determined using the
memcg_from_slab_page() function, which looks at
page->slab_cache->memcg_params.memcg .  In this case, using
mod_memcg_page_state() (as in account_kernel_stack()) is incorrect:
page->mem_cgroup pointer is NULL even for pages charged to a non-root
memory cgroup.

It can lead to kernel_stack per-memcg counters permanently showing 0 on
some architectures (depending on the configuration).

In order to fix it, let's introduce a mod_memcg_obj_state() helper, which
takes a pointer to a kernel object as a first argument, uses
mem_cgroup_from_obj() to get a RCU-protected memcg pointer and calls
mod_memcg_state().  It allows to handle all possible configurations
(CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE values) without
spilling any memcg/kmem specifics into fork.c .

Note: This is a special version of the patch created for stable
backports. It contains code from the following two patches:
  - mm: memcg/slab: introduce mem_cgroup_from_obj()
  - mm: fork: fix kernel_stack memcg stats for various stack implementations

Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: stable@vger.kernel.org
---
 include/linux/memcontrol.h | 12 ++++++++++++
 kernel/fork.c              |  4 ++--
 mm/memcontrol.c            | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a7a0a1a5c8d5..e9ba01336d4e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -695,6 +695,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 			int val);
 void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val);
+void mod_memcg_obj_state(void *p, int idx, int val);
 
 static inline void mod_lruvec_state(struct lruvec *lruvec,
 				    enum node_stat_item idx, int val)
@@ -1123,6 +1124,10 @@ static inline void __mod_lruvec_slab_state(void *p, enum node_stat_item idx,
 	__mod_node_page_state(page_pgdat(page), idx, val);
 }
 
+static inline void mod_memcg_obj_state(void *p, int idx, int val)
+{
+}
+
 static inline
 unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
 					    gfp_t gfp_mask,
@@ -1427,6 +1432,8 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg)
 	return memcg ? memcg->kmemcg_id : -1;
 }
 
+struct mem_cgroup *mem_cgroup_from_obj(void *p);
+
 #else
 
 static inline int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
@@ -1468,6 +1475,11 @@ static inline void memcg_put_cache_ids(void)
 {
 }
 
+static inline struct mem_cgroup *mem_cgroup_from_obj(void *p)
+{
+       return NULL;
+}
+
 #endif /* CONFIG_MEMCG_KMEM */
 
 #endif /* _LINUX_MEMCONTROL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 080809560072..183a6722dfe2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -397,8 +397,8 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
 		mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB,
 				    THREAD_SIZE / 1024 * account);
 
-		mod_memcg_page_state(first_page, MEMCG_KERNEL_STACK_KB,
-				     account * (THREAD_SIZE / 1024));
+		mod_memcg_obj_state(stack, MEMCG_KERNEL_STACK_KB,
+				    account * (THREAD_SIZE / 1024));
 	}
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6c83cf4ed970..a0aa1c213231 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -775,6 +775,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
 	rcu_read_unlock();
 }
 
+void mod_memcg_obj_state(void *p, int idx, int val)
+{
+	struct mem_cgroup *memcg;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_obj(p);
+	if (memcg)
+		mod_memcg_state(memcg, idx, val);
+	rcu_read_unlock();
+}
+
 /**
  * __count_memcg_events - account VM events in a cgroup
  * @memcg: the memory cgroup
@@ -2636,6 +2647,33 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
 }
 
 #ifdef CONFIG_MEMCG_KMEM
+/*
+ * Returns a pointer to the memory cgroup to which the kernel object is charged.
+ *
+ * The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(),
+ * cgroup_mutex, etc.
+ */
+struct mem_cgroup *mem_cgroup_from_obj(void *p)
+{
+	struct page *page;
+
+	if (mem_cgroup_disabled())
+		return NULL;
+
+	page = virt_to_head_page(p);
+
+	/*
+	 * Slab pages don't have page->mem_cgroup set because corresponding
+	 * kmem caches can be reparented during the lifetime. That's why
+	 * memcg_from_slab_page() should be used instead.
+	 */
+	if (PageSlab(page))
+		return memcg_from_slab_page(page);
+
+	/* All other pages use page->mem_cgroup */
+	return page->mem_cgroup;
+}
+
 static int memcg_alloc_cache_id(void)
 {
 	int id, size;
-- 
2.25.1

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Andrew Morton]

On Mon, 23 Mar 2020 17:42:21 -0700 Roman Gushchin <guro@fb.com> wrote:

> How about this one? I've merged them into one and stripped it a little bit.
> 
> Thanks!
> 

Yes, that looks good.  Here's the delta from the previously reviewed
version.  I think it's valid to retain those acks and revewed-by's.


From: Roman Gushchin <guro@fb.com>
Subject: mm: fork: fix kernel_stack memcg stats for various stack implementations

--- a/include/linux/memcontrol.h~mm-fork-fix-kernel_stack-memcg-stats-for-various-stack-implementations-v2
+++ a/include/linux/memcontrol.h
@@ -1432,6 +1432,8 @@ static inline int memcg_cache_id(struct
 	return memcg ? memcg->kmemcg_id : -1;
 }
 
+struct mem_cgroup *mem_cgroup_from_obj(void *p);
+
 #else
 
 static inline int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
@@ -1473,6 +1475,11 @@ static inline void memcg_put_cache_ids(v
 {
 }
 
+static inline struct mem_cgroup *mem_cgroup_from_obj(void *p)
+{
+       return NULL;
+}
+
 #endif /* CONFIG_MEMCG_KMEM */
 
 #endif /* _LINUX_MEMCONTROL_H */
--- a/mm/memcontrol.c~mm-fork-fix-kernel_stack-memcg-stats-for-various-stack-implementations-v2
+++ a/mm/memcontrol.c
@@ -2672,6 +2672,33 @@ static void commit_charge(struct page *p
 }
 
 #ifdef CONFIG_MEMCG_KMEM
+/*
+ * Returns a pointer to the memory cgroup to which the kernel object is charged.
+ *
+ * The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(),
+ * cgroup_mutex, etc.
+ */
+struct mem_cgroup *mem_cgroup_from_obj(void *p)
+{
+	struct page *page;
+
+	if (mem_cgroup_disabled())
+		return NULL;
+
+	page = virt_to_head_page(p);
+
+	/*
+	 * Slab pages don't have page->mem_cgroup set because corresponding
+	 * kmem caches can be reparented during the lifetime. That's why
+	 * memcg_from_slab_page() should be used instead.
+	 */
+	if (PageSlab(page))
+		return memcg_from_slab_page(page);
+
+	/* All other pages use page->mem_cgroup */
+	return page->mem_cgroup;
+}
+
 static int memcg_alloc_cache_id(void)
 {
 	int id, size;
_

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Andrew Morton]

On Mon, 23 Mar 2020 18:03:58 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 23 Mar 2020 17:42:21 -0700 Roman Gushchin <guro@fb.com> wrote:
> 
> > How about this one? I've merged them into one and stripped it a little bit.
> > 
> > Thanks!
> > 
> 
> Yes, that looks good.  Here's the delta from the previously reviewed
> version.  I think it's valid to retain those acks and revewed-by's.
> 
> 

And here's the altered "mm: memcg/slab: introduce
mem_cgroup_from_obj()", which I have renamed to "mm: memcg/slab: use
mem_cgroup_from_obj()":

The end result is slightly different - mem_cgroup_from_obj() will now
end up inside #ifdef CONFIG_MEMCG_KMEM.  Should I undo that?


From: Roman Gushchin <guro@fb.com>
Subject: mm: memcg/slab: use mem_cgroup_from_obj()

Sometimes we need to get a memcg pointer from a charged kernel object. 
The right way to get it depends on whether it's a proper slab object or
it's backed by raw pages (e.g.  it's a vmalloc alloction).  In the first
case the kmem_cache->memcg_params.memcg indirection should be used; in
other cases it's just page->mem_cgroup.

To simplify this task and hide the implementation details let's use the
mem_cgroup_from_obj() helper, which takes a pointer to any kernel object
and returns a valid memcg pointer or NULL.

Passing a kernel address rather than a pointer to a page will allow to use
this helper for per-object (rather than per-page) tracked objects in the
future.

The caller is still responsible to ensure that the returned memcg isn't
going away underneath: take the rcu read lock, cgroup mutex etc; depending
on the context.

mem_cgroup_from_kmem() defined in mm/list_lru.c is now obsolete and can be
removed.

Link: http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/list_lru.c   |   12 +-----------
 mm/memcontrol.c |    5 ++---
 2 files changed, 3 insertions(+), 14 deletions(-)

--- a/mm/list_lru.c~mm-memcg-slab-introduce-mem_cgroup_from_obj
+++ a/mm/list_lru.c
@@ -57,16 +57,6 @@ 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 memcg_from_slab_page(page);
-}
-
 static inline struct list_lru_one *
 list_lru_from_kmem(struct list_lru_node *nlru, void *ptr,
 		   struct mem_cgroup **memcg_ptr)
@@ -77,7 +67,7 @@ list_lru_from_kmem(struct list_lru_node
 	if (!nlru->memcg_lrus)
 		goto out;
 
-	memcg = mem_cgroup_from_kmem(ptr);
+	memcg = mem_cgroup_from_obj(ptr);
 	if (!memcg)
 		goto out;
 
--- a/mm/memcontrol.c~mm-memcg-slab-introduce-mem_cgroup_from_obj
+++ a/mm/memcontrol.c
@@ -759,13 +759,12 @@ void __mod_lruvec_state(struct lruvec *l
 
 void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val)
 {
-	struct page *page = virt_to_head_page(p);
-	pg_data_t *pgdat = page_pgdat(page);
+	pg_data_t *pgdat = page_pgdat(virt_to_page(p));
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
 	rcu_read_lock();
-	memcg = memcg_from_slab_page(page);
+	memcg = mem_cgroup_from_obj(p);
 
 	/* Untracked pages have no memcg, no lruvec. Update only the node */
 	if (!memcg || memcg == root_mem_cgroup) {
_

Re: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

[Andrew Morton]

On Mon, 23 Mar 2020 18:06:33 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:

> And here's the altered "mm: memcg/slab: introduce
> mem_cgroup_from_obj()", which I have renamed to "mm: memcg/slab: use
> mem_cgroup_from_obj()":
> 
> The end result is slightly different - mem_cgroup_from_obj() will now
> end up inside #ifdef CONFIG_MEMCG_KMEM.  Should I undo that?

err, no, we've just fed forward the build fixes in
mm-memcg-slab-introduce-mem_cgroup_from_obj-v2.patch so I think we're
all good.