On Tue, Mar 2, 2021 at 9:15 AM Roman Gushchin [off-list ref] wrote:

On Mon, Mar 01, 2021 at 02:22:26PM +0800, Muchun Song wrote:

quoted

The remote memcg charing APIs is a mechanism to charge kernel memory
to a given memcg. So we can move the infrastructure to the scope of
the CONFIG_MEMCG_KMEM.

This is not a good idea, because there is nothing kmem-specific
in the idea of remote charging, and we definitely will see cases
when user memory is charged to the process different from the current.

Got it. Thanks for your reminder.

quoted

As a bonus, on !CONFIG_MEMCG_KMEM build some functions and variables
can be compiled out.

Signed-off-by: Muchun Song <redacted>
---
 include/linux/sched.h    | 2 ++
 include/linux/sched/mm.h | 2 +-
 kernel/fork.c            | 2 +-
 mm/memcontrol.c          | 4 ++++
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ee46f5cab95b..c2d488eddf85 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h

@@ -1314,7 +1314,9 @@ struct task_struct {

      /* Number of pages to reclaim on returning to userland: */
      unsigned int                    memcg_nr_pages_over_high;
+#endif

+#ifdef CONFIG_MEMCG_KMEM
      /* Used by memcontrol for targeted memcg charge: */
      struct mem_cgroup               *active_memcg;
 #endif

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 1ae08b8462a4..64a72975270e 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h

@@ -294,7 +294,7 @@ static inline void memalloc_nocma_restore(unsigned int flags)
 }
 #endif

-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_KMEM
 DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg);
 /**
  * set_active_memcg - Starts the remote memcg charging scope.

diff --git a/kernel/fork.c b/kernel/fork.c
index d66cd1014211..d66718bc82d5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c

@@ -942,7 +942,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
      tsk->use_memdelay = 0;
 #endif

-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_KMEM
      tsk->active_memcg = NULL;
 #endif
      return tsk;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 39cb8c5bf8b2..092dc4588b43 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -76,8 +76,10 @@ EXPORT_SYMBOL(memory_cgrp_subsys);

 struct mem_cgroup *root_mem_cgroup __read_mostly;

+#ifdef CONFIG_MEMCG_KMEM
 /* Active memory cgroup to use from an interrupt context */
 DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg);
+#endif

 /* Socket memory accounting disabled? */
 static bool cgroup_memory_nosocket;

@@ -1054,6 +1056,7 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
 }
 EXPORT_SYMBOL(get_mem_cgroup_from_mm);

+#ifdef CONFIG_MEMCG_KMEM
 static __always_inline struct mem_cgroup *active_memcg(void)
 {
      if (in_interrupt())

@@ -1074,6 +1077,7 @@ static __always_inline bool memcg_kmem_bypass(void)

      return false;
 }
+#endif

 /**
  * mem_cgroup_iter - iterate over memory cgroup hierarchy
--

2.11.0