memcg: workingset: remove folio_memcg_rcu usage

The function workingset_activation() is called from folio_mark_accessed() with the guarantee that the given folio can not be freed under us in workingset_activation(). In addition, the association of the folio and its memcg can not be broken here because charge migration is no more. There is no need to use folio_memcg_rcu. Simply use folio_memcg_charged() because that is what this function cares about.

Signed-off-by Shakeel Butt <[email protected]>

Suggested-by Yu Zhao <[email protected]>

---

Andrew, please put this patch after the charge migration deprecation series.

 include/linux/memcontrol.h | 35 -----------------------------------
 mm/workingset.c            | 10 ++--------
 2 files changed, 2 insertions(+), 43 deletions(-)

include/linux/memcontrol.h +0 -35

index 932534291ca2..89a1e9f10e1b 100644
@@ -443,35 +443,6 @@ static inline bool folio_memcg_charged(struct folio *folio)
        return __folio_memcg(folio) != NULL;
 }
 
-/**
- * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
- * @folio: Pointer to the folio.
- *
- * This function assumes that the folio is known to have a
- * proper memory cgroup pointer. It's not safe to call this function
- * against some type of folios, e.g. slab folios or ex-slab folios.
- *
- * Return: A pointer to the memory cgroup associated with the folio,
- * or NULL.
- */
-static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
-{
-       unsigned long memcg_data = READ_ONCE(folio->memcg_data);
-
-       VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
-
-       if (memcg_data & MEMCG_DATA_KMEM) {
-               struct obj_cgroup *objcg;
-
-               objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
-               return obj_cgroup_memcg(objcg);
-       }
-
-       WARN_ON_ONCE(!rcu_read_lock_held());
-
-       return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
-}
-
 /*
  * folio_memcg_check - Get the memory cgroup associated with a folio.
  * @folio: Pointer to the folio.

@@ -1084,12 +1055,6 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
        return NULL;
 }
 
-static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
-{
-       WARN_ON_ONCE(!rcu_read_lock_held());
-       return NULL;
-}
-
 static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
 {
        return NULL;

mm/workingset.c +0 -3

index 4b58ef535a17..c47aa482fad5 100644
@@ -591,9 +591,6 @@ void workingset_refault(struct folio *folio, void *shadow)
  */
 void workingset_activation(struct folio *folio)
 {
-       struct mem_cgroup *memcg;
-
-       rcu_read_lock();
        /*
         * Filter non-memcg pages here, e.g. unmap can call
         * mark_page_accessed() on VDSO pages.

mm/workingset.c +0 -3

-out:
-       rcu_read_unlock();
 }
 
 /*
--

2.43.5

Quoted 88 lines · Shakeel Butt

The function workingset_activation() is called from folio_mark_accessed() with the guarantee that the given folio can not be freed under us in workingset_activation(). In addition, the association of the folio and its memcg can not be broken here because charge migration is no more. There is no need to use folio_memcg_rcu. Simply use folio_memcg_charged() because that is what this function cares about.

Signed-off-by Shakeel Butt <[email protected]>

Suggested-by Yu Zhao <[email protected]>

---

Andrew, please put this patch after the charge migration deprecation series.

 include/linux/memcontrol.h | 35 -----------------------------------
 mm/workingset.c            | 10 ++--------
 2 files changed, 2 insertions(+), 43 deletions(-)

include/linux/memcontrol.h +0 -35

index 932534291ca2..89a1e9f10e1b 100644
@@ -443,35 +443,6 @@ static inline bool folio_memcg_charged(struct folio *folio)
        return __folio_memcg(folio) != NULL;
 }
 
-/**
- * folio_memcg_rcu - Locklessly get the memory cgroup associated with a folio.
- * @folio: Pointer to the folio.
- *
- * This function assumes that the folio is known to have a
- * proper memory cgroup pointer. It's not safe to call this function
- * against some type of folios, e.g. slab folios or ex-slab folios.
- *
- * Return: A pointer to the memory cgroup associated with the folio,
- * or NULL.
- */
-static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
-{
-       unsigned long memcg_data = READ_ONCE(folio->memcg_data);
-
-       VM_BUG_ON_FOLIO(folio_test_slab(folio), folio);
-
-       if (memcg_data & MEMCG_DATA_KMEM) {
-               struct obj_cgroup *objcg;
-
-               objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
-               return obj_cgroup_memcg(objcg);
-       }
-
-       WARN_ON_ONCE(!rcu_read_lock_held());
-
-       return (struct mem_cgroup *)(memcg_data & ~OBJEXTS_FLAGS_MASK);
-}
-
 /*
  * folio_memcg_check - Get the memory cgroup associated with a folio.
  * @folio: Pointer to the folio.

@@ -1084,12 +1055,6 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
        return NULL;
 }
 
-static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
-{
-       WARN_ON_ONCE(!rcu_read_lock_held());
-       return NULL;
-}
-
 static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
 {
        return NULL;

mm/workingset.c +0 -3

index 4b58ef535a17..c47aa482fad5 100644
@@ -591,9 +591,6 @@ void workingset_refault(struct folio *folio, void *shadow)
  */
 void workingset_activation(struct folio *folio)
 {
-       struct mem_cgroup *memcg;
-
-       rcu_read_lock();
        /*
         * Filter non-memcg pages here, e.g. unmap can call
         * mark_page_accessed() on VDSO pages.

mm/workingset.c void workingset_activation(struct folio *folio) · line 599

Quoted 2 lines

mm/workingset.c +0 -0

@@ -601,12 +598,9 @@ void workingset_activation(struct folio *folio)
         * XXX: See workingset_refault() - this should return
         * root_mem_cgroup even for !CONFIG_MEMCG.

The "XXX" part of the comments doesn't apply anymore.

mm/workingset.c void workingset_activation(struct folio *folio) · line 603

Quoted 7 lines

mm/workingset.c +2 -3

         */
-       memcg = folio_memcg_rcu(folio);
-       if (!mem_cgroup_disabled() && !memcg)
-               goto out;
+       if (mem_cgroup_disabled() || !folio_memcg_charged(folio))
+               return;
        workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));

if (mem_cgroup_disabled() || folio_memcg_charged(folio))
workingset_age_nonresident()

We still want to call workingset_age_nonresident() when memcg is disabled. (We just want to "Filter non-memcg pages here" when memcg is enabled, as the comment above says, which I assume still applies?)