[PATCH RFC 4/4] mm: kmem: enable kernel memcg accounting from interrupt contexts

[Roman Gushchin <guro@fb.com>]

If a memcg to charge can be determined (using remote charging API),
there are no reasons to exclude allocations made from an interrupt
context from the accounting.

Such allocations will pass even if the resulting memcg size will
exceed the hard limit, but it will affect the application of the
memory pressure and an inability to put the workload under the limit
will eventually trigger the OOM.

To use active_memcg() helper, memcg_kmem_bypass() is moved back
to memcontrol.c.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 include/linux/memcontrol.h | 12 ------------
 mm/memcontrol.c            | 13 +++++++++++++
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d0b036123c6a..924177502479 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1528,18 +1528,6 @@ static inline bool memcg_kmem_enabled(void)
 	return static_branch_likely(&memcg_kmem_enabled_key);
 }
 
-static inline bool memcg_kmem_bypass(void)
-{
-	if (in_interrupt())
-		return true;
-
-	/* Allow remote memcg charging in kthread contexts. */
-	if ((!current->mm || (current->flags & PF_KTHREAD)) &&
-	     !current->active_memcg)
-		return true;
-	return false;
-}
-
 static inline int memcg_kmem_charge_page(struct page *page, gfp_t gfp,
 					 int order)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a51a6066079e..75cd1a1e66c8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1098,6 +1098,19 @@ static __always_inline struct mem_cgroup *get_active_memcg(void)
 	return memcg;
 }
 
+static __always_inline bool memcg_kmem_bypass(void)
+{
+	/* Allow remote memcg charging from any context. */
+	if (unlikely(active_memcg()))
+		return false;
+
+	/* Memcg to charge can't be determined. */
+	if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD))
+		return true;
+
+	return false;
+}
+
 /**
  * If active memcg is set, do not fallback to current->mm->memcg.
  */
-- 
2.26.2