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authorThomas Gleixner <tglx@linutronix.de>2021-09-28 14:24:32 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-10-05 15:52:09 +0200
commit8d491de6edc27138806cae6e8eca455beb325b62 (patch)
tree63a9b2be7c7f2baacc8dfd695088634fd1c8d079 /include/linux/sched
parentd07b2eee4501c393cbf5bfcad36143310cfd72f9 (diff)
sched: Move mmdrop to RCU on RT
mmdrop() is invoked from finish_task_switch() by the incoming task to drop the mm which was handed over by the previous task. mmdrop() can be quite expensive which prevents an incoming real-time task from getting useful work done. Provide mmdrop_sched() which maps to mmdrop() on !RT kernels. On RT kernels it delagates the eventually required invocation of __mmdrop() to RCU. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210928122411.648582026@linutronix.de
Diffstat (limited to 'include/linux/sched')
-rw-r--r--include/linux/sched/mm.h29
1 files changed, 29 insertions, 0 deletions
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 5561486fddef..aca874d33fe6 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -49,6 +49,35 @@ static inline void mmdrop(struct mm_struct *mm)
__mmdrop(mm);
}
+#ifdef CONFIG_PREEMPT_RT
+/*
+ * RCU callback for delayed mm drop. Not strictly RCU, but call_rcu() is
+ * by far the least expensive way to do that.
+ */
+static inline void __mmdrop_delayed(struct rcu_head *rhp)
+{
+ struct mm_struct *mm = container_of(rhp, struct mm_struct, delayed_drop);
+
+ __mmdrop(mm);
+}
+
+/*
+ * Invoked from finish_task_switch(). Delegates the heavy lifting on RT
+ * kernels via RCU.
+ */
+static inline void mmdrop_sched(struct mm_struct *mm)
+{
+ /* Provides a full memory barrier. See mmdrop() */
+ if (atomic_dec_and_test(&mm->mm_count))
+ call_rcu(&mm->delayed_drop, __mmdrop_delayed);
+}
+#else
+static inline void mmdrop_sched(struct mm_struct *mm)
+{
+ mmdrop(mm);
+}
+#endif
+
/**
* mmget() - Pin the address space associated with a &struct mm_struct.
* @mm: The address space to pin.