From 558ce6646445d203f70d8ae912cf4abb7f0e34d6 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Sat, 14 Feb 2015 10:05:23 -0600
Subject: [PATCH 13/13] Turn mmput into an async function

mmput() is part of the process exit() path as well as many
other parts of the kernel.  The actual work (when count
hits 0) typically is part of exit() but can happen in all
other cases as well (due to something opening files in
/proc/<pid>/ for example).

In the exit() path, the common case, this happens before
the parent is notified currently, which means that the
time mmput() takes delays the parent from doing more work.
(say, make that wants to call another copy of gcc).

The cost of mmput() can be considerable, it will go all the
way into graphics drivers etc etc... so turning this async
will take this cost out of the latency sensitive path.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
---
 kernel/fork.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 03c1eaa..6518e93 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -74,6 +74,7 @@
 #include <linux/uprobes.h>
 #include <linux/aio.h>
 #include <linux/compiler.h>
+#include <linux/async.h>
 #include <linux/sysctl.h>
 
 #include <asm/pgtable.h>
@@ -680,6 +681,26 @@ void __mmdrop(struct mm_struct *mm)
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
 
+
+static void mmput_async(void *data, async_cookie_t cookie)
+{
+	struct mm_struct *mm = data;
+	uprobe_clear_state(mm);
+	exit_aio(mm);
+	ksm_exit(mm);
+	khugepaged_exit(mm); /* must run before exit_mmap */
+	exit_mmap(mm);
+	set_mm_exe_file(mm, NULL);
+	if (!list_empty(&mm->mmlist)) {
+		spin_lock(&mmlist_lock);
+		list_del(&mm->mmlist);
+		spin_unlock(&mmlist_lock);
+	}
+	if (mm->binfmt)
+		module_put(mm->binfmt->module);
+	mmdrop(mm);
+}
+
 /*
  * Decrement the use count and release all resources for an mm.
  */
@@ -687,22 +708,8 @@ void mmput(struct mm_struct *mm)
 {
 	might_sleep();
 
-	if (atomic_dec_and_test(&mm->mm_users)) {
-		uprobe_clear_state(mm);
-		exit_aio(mm);
-		ksm_exit(mm);
-		khugepaged_exit(mm); /* must run before exit_mmap */
-		exit_mmap(mm);
-		set_mm_exe_file(mm, NULL);
-		if (!list_empty(&mm->mmlist)) {
-			spin_lock(&mmlist_lock);
-			list_del(&mm->mmlist);
-			spin_unlock(&mmlist_lock);
-		}
-		if (mm->binfmt)
-			module_put(mm->binfmt->module);
-		mmdrop(mm);
-	}
+	if (atomic_dec_and_test(&mm->mm_users))
+		async_schedule(mmput_async, mm);
 }
 EXPORT_SYMBOL_GPL(mmput);
 
-- 
2.4.4