[PATCH -next v3 0/2] memcg cleanups

[PATCH -next v3 0/2] memcg cleanups

[Chen Ridong]

From: Chen Ridong <chenridong@huawei.com>

1/2 moves mem_cgroup_usage() to memcontrol-v1.c
2/2 removes mem_cgroup_size()

Both are code moves/removals with no behavior change.

---

Change from v2:
1. get usage via mem_cgroup_protection and eliminate ifdef.

Chen Ridong (2):
  memcg: move mem_cgroup_usage memcontrol-v1.c
  memcg: remove mem_cgroup_size()

 include/linux/memcontrol.h | 18 +++++++-----------
 mm/memcontrol-v1.c         | 22 ++++++++++++++++++++++
 mm/memcontrol-v1.h         |  2 --
 mm/memcontrol.c            | 27 ---------------------------
 mm/vmscan.c                |  9 ++++-----
 5 files changed, 33 insertions(+), 45 deletions(-)

-- 
2.34.1

[PATCH -next v3 1/2] memcg: move mem_cgroup_usage memcontrol-v1.c

[Chen Ridong]

From: Chen Ridong <chenridong@huawei.com>

Currently, mem_cgroup_usage is only used for v1, just move it to
memcontrol-v1.c

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol-v1.c | 22 ++++++++++++++++++++++
 mm/memcontrol-v1.h |  2 --
 mm/memcontrol.c    | 22 ----------------------
 3 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index 6eed14bff742..0b50cb122ff3 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -427,6 +427,28 @@ static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
 }
 #endif
 
+static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
+{
+	unsigned long val;
+
+	if (mem_cgroup_is_root(memcg)) {
+		/*
+		 * Approximate root's usage from global state. This isn't
+		 * perfect, but the root usage was always an approximation.
+		 */
+		val = global_node_page_state(NR_FILE_PAGES) +
+			global_node_page_state(NR_ANON_MAPPED);
+		if (swap)
+			val += total_swap_pages - get_nr_swap_pages();
+	} else {
+		if (!swap)
+			val = page_counter_read(&memcg->memory);
+		else
+			val = page_counter_read(&memcg->memsw);
+	}
+	return val;
+}
+
 static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
 {
 	struct mem_cgroup_threshold_ary *t;
diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index 6358464bb416..e92b21af92b1 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -22,8 +22,6 @@
 	     iter != NULL;				\
 	     iter = mem_cgroup_iter(NULL, iter, NULL))
 
-unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
-
 void drain_all_stock(struct mem_cgroup *root_memcg);
 
 unsigned long memcg_events(struct mem_cgroup *memcg, int event);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e2e49f4ec9e0..dbe7d8f93072 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3272,28 +3272,6 @@ void folio_split_memcg_refs(struct folio *folio, unsigned old_order,
 	css_get_many(&__folio_memcg(folio)->css, new_refs);
 }
 
-unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
-{
-	unsigned long val;
-
-	if (mem_cgroup_is_root(memcg)) {
-		/*
-		 * Approximate root's usage from global state. This isn't
-		 * perfect, but the root usage was always an approximation.
-		 */
-		val = global_node_page_state(NR_FILE_PAGES) +
-			global_node_page_state(NR_ANON_MAPPED);
-		if (swap)
-			val += total_swap_pages - get_nr_swap_pages();
-	} else {
-		if (!swap)
-			val = page_counter_read(&memcg->memory);
-		else
-			val = page_counter_read(&memcg->memsw);
-	}
-	return val;
-}
-
 static int memcg_online_kmem(struct mem_cgroup *memcg)
 {
 	struct obj_cgroup *objcg;
-- 
2.34.1

Re: [PATCH -next v3 1/2] memcg: move mem_cgroup_usage memcontrol-v1.c

[Shakeel Butt]

On Thu, Dec 11, 2025 at 01:30:18AM +0000, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> Currently, mem_cgroup_usage is only used for v1, just move it to
> memcontrol-v1.c
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH -next v3 1/2] memcg: move mem_cgroup_usage memcontrol-v1.c

[Michal Koutný]

[-- Attachment #1: Type: text/plain, Size: 620 bytes --]

On Thu, Dec 11, 2025 at 01:30:18AM +0000, Chen Ridong <chenridong@huaweicloud.com> wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> Currently, mem_cgroup_usage is only used for v1, just move it to
> memcontrol-v1.c
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  mm/memcontrol-v1.c | 22 ++++++++++++++++++++++
>  mm/memcontrol-v1.h |  2 --
>  mm/memcontrol.c    | 22 ----------------------
>  3 files changed, 22 insertions(+), 24 deletions(-)

Acked-by: Michal Koutný <mkoutny@suse.com>

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[PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Chen Ridong]

From: Chen Ridong <chenridong@huawei.com>

The mem_cgroup_size helper is used only in apply_proportional_protection
to read the current memory usage. Its semantics are unclear and
inconsistent with other sites, which directly call page_counter_read for
the same purpose.

Remove this helper and get its usage via mem_cgroup_protection for
clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
to better reflect its meaning.

No functional changes intended.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
---
 include/linux/memcontrol.h | 18 +++++++-----------
 mm/memcontrol.c            |  5 -----
 mm/vmscan.c                |  9 ++++-----
 3 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6a48398a1f4e..603252e3169c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -557,13 +557,15 @@ static inline bool mem_cgroup_disabled(void)
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
-					 unsigned long *low)
+					 unsigned long *low,
+					 unsigned long *usage)
 {
-	*min = *low = 0;
+	*min = *low = *usage = 0;
 
 	if (mem_cgroup_disabled())
 		return;
 
+	*usage = page_counter_read(&memcg->memory);
 	/*
 	 * There is no reclaim protection applied to a targeted reclaim.
 	 * We are special casing this specific case here because
@@ -919,8 +921,6 @@ static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
 
-unsigned long mem_cgroup_size(struct mem_cgroup *memcg);
-
 void mem_cgroup_print_oom_context(struct mem_cgroup *memcg,
 				struct task_struct *p);
 
@@ -1102,9 +1102,10 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
-					 unsigned long *low)
+					 unsigned long *low,
+					 unsigned long *usage)
 {
-	*min = *low = 0;
+	*min = *low = *usage = 0;
 }
 
 static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
@@ -1328,11 +1329,6 @@ static inline unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 	return 0;
 }
 
-static inline unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
-{
-	return 0;
-}
-
 static inline void
 mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *p)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dbe7d8f93072..659ce171b1b3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1621,11 +1621,6 @@ unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 	return max;
 }
 
-unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
-{
-	return page_counter_read(&memcg->memory);
-}
-
 void __memcg_memory_event(struct mem_cgroup *memcg,
 			  enum memcg_memory_event event, bool allow_spinning)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 670fe9fae5ba..9a6ee80275fc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2451,9 +2451,9 @@ static inline void calculate_pressure_balance(struct scan_control *sc,
 static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		struct scan_control *sc, unsigned long scan)
 {
-	unsigned long min, low;
+	unsigned long min, low, usage;
 
-	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
+	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low, &usage);
 
 	if (min || low) {
 		/*
@@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		 * again by how much of the total memory used is under
 		 * hard protection.
 		 */
-		unsigned long cgroup_size = mem_cgroup_size(memcg);
 		unsigned long protection;
 
 		/* memory.low scaling, make sure we retry before OOM */
@@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		}
 
 		/* Avoid TOCTOU with earlier protection check */
-		cgroup_size = max(cgroup_size, protection);
+		usage = max(usage, protection);
 
-		scan -= scan * protection / (cgroup_size + 1);
+		scan -= scan * protection / (usage + 1);
 
 		/*
 		 * Minimally target SWAP_CLUSTER_MAX pages to keep
-- 
2.34.1

Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Johannes Weiner]

On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>

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

Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Michal Hocko]

On Thu 11-12-25 01:30:19, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>

Yes, this looks much better.
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  include/linux/memcontrol.h | 18 +++++++-----------
>  mm/memcontrol.c            |  5 -----
>  mm/vmscan.c                |  9 ++++-----
>  3 files changed, 11 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6a48398a1f4e..603252e3169c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -557,13 +557,15 @@ static inline bool mem_cgroup_disabled(void)
>  static inline void mem_cgroup_protection(struct mem_cgroup *root,
>  					 struct mem_cgroup *memcg,
>  					 unsigned long *min,
> -					 unsigned long *low)
> +					 unsigned long *low,
> +					 unsigned long *usage)
>  {
> -	*min = *low = 0;
> +	*min = *low = *usage = 0;
>  
>  	if (mem_cgroup_disabled())
>  		return;
>  
> +	*usage = page_counter_read(&memcg->memory);
>  	/*
>  	 * There is no reclaim protection applied to a targeted reclaim.
>  	 * We are special casing this specific case here because
> @@ -919,8 +921,6 @@ static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
>  
>  unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
>  
> -unsigned long mem_cgroup_size(struct mem_cgroup *memcg);
> -
>  void mem_cgroup_print_oom_context(struct mem_cgroup *memcg,
>  				struct task_struct *p);
>  
> @@ -1102,9 +1102,10 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
>  static inline void mem_cgroup_protection(struct mem_cgroup *root,
>  					 struct mem_cgroup *memcg,
>  					 unsigned long *min,
> -					 unsigned long *low)
> +					 unsigned long *low,
> +					 unsigned long *usage)
>  {
> -	*min = *low = 0;
> +	*min = *low = *usage = 0;
>  }
>  
>  static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
> @@ -1328,11 +1329,6 @@ static inline unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>  	return 0;
>  }
>  
> -static inline unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
> -{
> -	return 0;
> -}
> -
>  static inline void
>  mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *p)
>  {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index dbe7d8f93072..659ce171b1b3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1621,11 +1621,6 @@ unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
>  	return max;
>  }
>  
> -unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
> -{
> -	return page_counter_read(&memcg->memory);
> -}
> -
>  void __memcg_memory_event(struct mem_cgroup *memcg,
>  			  enum memcg_memory_event event, bool allow_spinning)
>  {
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 670fe9fae5ba..9a6ee80275fc 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2451,9 +2451,9 @@ static inline void calculate_pressure_balance(struct scan_control *sc,
>  static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		struct scan_control *sc, unsigned long scan)
>  {
> -	unsigned long min, low;
> +	unsigned long min, low, usage;
>  
> -	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
> +	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low, &usage);
>  
>  	if (min || low) {
>  		/*
> @@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		 * again by how much of the total memory used is under
>  		 * hard protection.
>  		 */
> -		unsigned long cgroup_size = mem_cgroup_size(memcg);
>  		unsigned long protection;
>  
>  		/* memory.low scaling, make sure we retry before OOM */
> @@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		}
>  
>  		/* Avoid TOCTOU with earlier protection check */
> -		cgroup_size = max(cgroup_size, protection);
> +		usage = max(usage, protection);
>  
> -		scan -= scan * protection / (cgroup_size + 1);
> +		scan -= scan * protection / (usage + 1);
>  
>  		/*
>  		 * Minimally target SWAP_CLUSTER_MAX pages to keep
> -- 
> 2.34.1

-- 
Michal Hocko
SUSE Labs

Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Shakeel Butt]

On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>

Acked-by: Shakeel Butt <shakeel.butt@linux.dev>

Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Michal Koutný]

[-- Attachment #1: Type: text/plain, Size: 1700 bytes --]

Hi Ridong.

On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong <chenridong@huaweicloud.com> wrote:
> From: Chen Ridong <chenridong@huawei.com>
> 
> The mem_cgroup_size helper is used only in apply_proportional_protection
> to read the current memory usage. Its semantics are unclear and
> inconsistent with other sites, which directly call page_counter_read for
> the same purpose.
> 
> Remove this helper and get its usage via mem_cgroup_protection for
> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
> to better reflect its meaning.
> 
> No functional changes intended.
> 
> Signed-off-by: Chen Ridong <chenridong@huawei.com>

Why does mem_cgroup_calculate_protection "calculate" usage for its
callers? Couldn't you just the change source in
apply_proportional_protection()?

Thanks,
Michal

> @@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		 * again by how much of the total memory used is under
>  		 * hard protection.
>  		 */
> -		unsigned long cgroup_size = mem_cgroup_size(memcg);
+		unsigned long cgroup_size = page_counter_read(memcg);

>  		unsigned long protection;
>  
>  		/* memory.low scaling, make sure we retry before OOM */
> @@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>  		}
>  
>  		/* Avoid TOCTOU with earlier protection check */
> -		cgroup_size = max(cgroup_size, protection);
> +		usage = max(usage, protection);
>  
> -		scan -= scan * protection / (cgroup_size + 1);
> +		scan -= scan * protection / (usage + 1);
>  
>  		/*
>  		 * Minimally target SWAP_CLUSTER_MAX pages to keep

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Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Chen Ridong]

On 2025/12/16 0:28, Michal Koutný wrote:
> Hi Ridong.
> 
> On Thu, Dec 11, 2025 at 01:30:19AM +0000, Chen Ridong <chenridong@huaweicloud.com> wrote:
>> From: Chen Ridong <chenridong@huawei.com>
>>
>> The mem_cgroup_size helper is used only in apply_proportional_protection
>> to read the current memory usage. Its semantics are unclear and
>> inconsistent with other sites, which directly call page_counter_read for
>> the same purpose.
>>
>> Remove this helper and get its usage via mem_cgroup_protection for
>> clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
>> to better reflect its meaning.
>>
>> No functional changes intended.
>>
>> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> 
> Why does mem_cgroup_calculate_protection "calculate" usage for its
> callers? Couldn't you just the change source in
> apply_proportional_protection()?
> 
> Thanks,
> Michal
> 

I apologize for missing this message earlier.

In my v2 patch, I was reading the usage directly:

+		unsigned long usage = page_counter_read(&memcg->memory);

This works fine when CONFIG_MEMCG=y, but fails to compile when memory cgroups are disabled. To
handle this, I initially added #ifdef CONFIG_MEMCG guards.

Following Johannes's suggestion, I have now moved this logic into mem_cgroup_protection() to
eliminate the #ifdef and keep the code cleaner.

Discussion:
https://lore.kernel.org/all/20251210163634.GB643576@cmpxchg.org/

>> @@ -2485,7 +2485,6 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>>  		 * again by how much of the total memory used is under
>>  		 * hard protection.
>>  		 */
>> -		unsigned long cgroup_size = mem_cgroup_size(memcg);
> +		unsigned long cgroup_size = page_counter_read(memcg);
> 
>>  		unsigned long protection;
>>  
>>  		/* memory.low scaling, make sure we retry before OOM */
>> @@ -2497,9 +2496,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
>>  		}
>>  
>>  		/* Avoid TOCTOU with earlier protection check */
>> -		cgroup_size = max(cgroup_size, protection);
>> +		usage = max(usage, protection);
>>  
>> -		scan -= scan * protection / (cgroup_size + 1);
>> +		scan -= scan * protection / (usage + 1);
>>  
>>  		/*
>>  		 * Minimally target SWAP_CLUSTER_MAX pages to keep

-- 
Best regards,
Ridong

Re: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

[Michal Koutný]

[-- Attachment #1: Type: text/plain, Size: 442 bytes --]

On Tue, Dec 16, 2025 at 08:34:40PM +0800, Chen Ridong <chenridong@huaweicloud.com> wrote:
> In my v2 patch, I was reading the usage directly:
> 
> +		unsigned long usage = page_counter_read(&memcg->memory);
> 
> This works fine when CONFIG_MEMCG=y, but fails to compile when memory cgroups are disabled. To
> handle this, I initially added #ifdef CONFIG_MEMCG guards.

Ah, !CONFIG_MEMCG, I get it now. Sorry for the noise.

Michal

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