[PATCH -next 0/2] memcg cleanups

[PATCH -next 0/2] memcg cleanups

[Chen Ridong]

From: Chen Ridong <chenridong@huawei.com>

This series cleans up two helpers in memcg:

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.

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

 include/linux/memcontrol.h |  7 -------
 mm/memcontrol-v1.c         | 22 ++++++++++++++++++++++
 mm/memcontrol-v1.h         |  2 --
 mm/memcontrol.c            | 27 ---------------------------
 mm/vmscan.c                |  6 +++---
 5 files changed, 25 insertions(+), 39 deletions(-)

-- 
2.34.1

[PATCH -next 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>
---
 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

[PATCH -next 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 replace its usage with page_counter_read for
clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
to better reflect its meaning.

This change is safe because page_counter_read() is only called when memcg
is enabled in the apply_proportional_protection.

No functional changes intended.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
---
 include/linux/memcontrol.h | 7 -------
 mm/memcontrol.c            | 5 -----
 mm/vmscan.c                | 6 +++---
 3 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6a48398a1f4e..bedeb606c691 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -919,8 +919,6 @@ 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);
 
@@ -1328,11 +1326,6 @@ 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..35175f7b7f6e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2485,7 +2485,7 @@ 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 usage = page_counter_read(&memcg->memory);
 		unsigned long protection;
 
 		/* memory.low scaling, make sure we retry before OOM */
@@ -2497,9 +2497,9 @@ 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 2/2] memcg: remove mem_cgroup_size()

[kernel test robot]

Hi Chen,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20251209]

url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/memcg-move-mem_cgroup_usage-memcontrol-v1-c/20251209-211854
base:   next-20251209
patch link:    https://lore.kernel.org/r/20251209130251.1988615-3-chenridong%40huaweicloud.com
patch subject: [PATCH -next 2/2] memcg: remove mem_cgroup_size()
config: i386-allnoconfig (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512100924.LqJqXM7P-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/vmscan.c: In function 'apply_proportional_protection':
>> mm/vmscan.c:2488:63: error: invalid use of undefined type 'struct mem_cgroup'
    2488 |                 unsigned long usage = page_counter_read(&memcg->memory);
         |                                                               ^~


vim +2488 mm/vmscan.c

  2450	
  2451	static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
  2452			struct scan_control *sc, unsigned long scan)
  2453	{
  2454		unsigned long min, low;
  2455	
  2456		mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
  2457	
  2458		if (min || low) {
  2459			/*
  2460			 * Scale a cgroup's reclaim pressure by proportioning
  2461			 * its current usage to its memory.low or memory.min
  2462			 * setting.
  2463			 *
  2464			 * This is important, as otherwise scanning aggression
  2465			 * becomes extremely binary -- from nothing as we
  2466			 * approach the memory protection threshold, to totally
  2467			 * nominal as we exceed it.  This results in requiring
  2468			 * setting extremely liberal protection thresholds. It
  2469			 * also means we simply get no protection at all if we
  2470			 * set it too low, which is not ideal.
  2471			 *
  2472			 * If there is any protection in place, we reduce scan
  2473			 * pressure by how much of the total memory used is
  2474			 * within protection thresholds.
  2475			 *
  2476			 * There is one special case: in the first reclaim pass,
  2477			 * we skip over all groups that are within their low
  2478			 * protection. If that fails to reclaim enough pages to
  2479			 * satisfy the reclaim goal, we come back and override
  2480			 * the best-effort low protection. However, we still
  2481			 * ideally want to honor how well-behaved groups are in
  2482			 * that case instead of simply punishing them all
  2483			 * equally. As such, we reclaim them based on how much
  2484			 * memory they are using, reducing the scan pressure
  2485			 * again by how much of the total memory used is under
  2486			 * hard protection.
  2487			 */
> 2488			unsigned long usage = page_counter_read(&memcg->memory);
  2489			unsigned long protection;
  2490	
  2491			/* memory.low scaling, make sure we retry before OOM */
  2492			if (!sc->memcg_low_reclaim && low > min) {
  2493				protection = low;
  2494				sc->memcg_low_skipped = 1;
  2495			} else {
  2496				protection = min;
  2497			}
  2498	
  2499			/* Avoid TOCTOU with earlier protection check */
  2500			usage = max(usage, protection);
  2501	
  2502			scan -= scan * protection / (usage + 1);
  2503	
  2504			/*
  2505			 * Minimally target SWAP_CLUSTER_MAX pages to keep
  2506			 * reclaim moving forwards, avoiding decrementing
  2507			 * sc->priority further than desirable.
  2508			 */
  2509			scan = max(scan, SWAP_CLUSTER_MAX);
  2510		}
  2511		return scan;
  2512	}
  2513	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[kernel test robot]

Hi Chen,

kernel test robot noticed the following build errors:

[auto build test ERROR on next-20251209]

url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/memcg-move-mem_cgroup_usage-memcontrol-v1-c/20251209-211854
base:   next-20251209
patch link:    https://lore.kernel.org/r/20251209130251.1988615-3-chenridong%40huaweicloud.com
patch subject: [PATCH -next 2/2] memcg: remove mem_cgroup_size()
config: arm-allnoconfig (https://download.01.org/0day-ci/archive/20251210/202512100939.F1LEdUev-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 6ec8c4351cfc1d0627d1633b02ea787bd29c77d8)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251210/202512100939.F1LEdUev-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512100939.F1LEdUev-lkp@intel.com/

All errors (new ones prefixed by >>):

>> mm/vmscan.c:2488:49: error: incomplete definition of type 'struct mem_cgroup'
    2488 |                 unsigned long usage = page_counter_read(&memcg->memory);
         |                                                          ~~~~~^
   include/linux/mm_types.h:36:8: note: forward declaration of 'struct mem_cgroup'
      36 | struct mem_cgroup;
         |        ^
   1 error generated.


vim +2488 mm/vmscan.c

  2450	
  2451	static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
  2452			struct scan_control *sc, unsigned long scan)
  2453	{
  2454		unsigned long min, low;
  2455	
  2456		mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
  2457	
  2458		if (min || low) {
  2459			/*
  2460			 * Scale a cgroup's reclaim pressure by proportioning
  2461			 * its current usage to its memory.low or memory.min
  2462			 * setting.
  2463			 *
  2464			 * This is important, as otherwise scanning aggression
  2465			 * becomes extremely binary -- from nothing as we
  2466			 * approach the memory protection threshold, to totally
  2467			 * nominal as we exceed it.  This results in requiring
  2468			 * setting extremely liberal protection thresholds. It
  2469			 * also means we simply get no protection at all if we
  2470			 * set it too low, which is not ideal.
  2471			 *
  2472			 * If there is any protection in place, we reduce scan
  2473			 * pressure by how much of the total memory used is
  2474			 * within protection thresholds.
  2475			 *
  2476			 * There is one special case: in the first reclaim pass,
  2477			 * we skip over all groups that are within their low
  2478			 * protection. If that fails to reclaim enough pages to
  2479			 * satisfy the reclaim goal, we come back and override
  2480			 * the best-effort low protection. However, we still
  2481			 * ideally want to honor how well-behaved groups are in
  2482			 * that case instead of simply punishing them all
  2483			 * equally. As such, we reclaim them based on how much
  2484			 * memory they are using, reducing the scan pressure
  2485			 * again by how much of the total memory used is under
  2486			 * hard protection.
  2487			 */
> 2488			unsigned long usage = page_counter_read(&memcg->memory);
  2489			unsigned long protection;
  2490	
  2491			/* memory.low scaling, make sure we retry before OOM */
  2492			if (!sc->memcg_low_reclaim && low > min) {
  2493				protection = low;
  2494				sc->memcg_low_skipped = 1;
  2495			} else {
  2496				protection = min;
  2497			}
  2498	
  2499			/* Avoid TOCTOU with earlier protection check */
  2500			usage = max(usage, protection);
  2501	
  2502			scan -= scan * protection / (usage + 1);
  2503	
  2504			/*
  2505			 * Minimally target SWAP_CLUSTER_MAX pages to keep
  2506			 * reclaim moving forwards, avoiding decrementing
  2507			 * sc->priority further than desirable.
  2508			 */
  2509			scan = max(scan, SWAP_CLUSTER_MAX);
  2510		}
  2511		return scan;
  2512	}
  2513	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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

[Chen Ridong]

On 2025/12/10 9:35, kernel test robot wrote:
> Hi Chen,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on next-20251209]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Chen-Ridong/memcg-move-mem_cgroup_usage-memcontrol-v1-c/20251209-211854
> base:   next-20251209
> patch link:    https://lore.kernel.org/r/20251209130251.1988615-3-chenridong%40huaweicloud.com
> patch subject: [PATCH -next 2/2] memcg: remove mem_cgroup_size()
> config: i386-allnoconfig (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-lkp@intel.com/config)
> compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251210/202512100924.LqJqXM7P-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202512100924.LqJqXM7P-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    mm/vmscan.c: In function 'apply_proportional_protection':
>>> mm/vmscan.c:2488:63: error: invalid use of undefined type 'struct mem_cgroup'
>     2488 |                 unsigned long usage = page_counter_read(&memcg->memory);
>          |                                                               ^~
> 
> 
> vim +2488 mm/vmscan.c
> 

Oh, I missed CONFIG_MEMCG=n case, will fix it, thanks.

-- 
Best regards,
Ridong