From: Davidlohr Bueso <davidlohr@hp.com>
Date: Thu, 22 May 2014 00:42:45 +0000 (+1000)
Subject: mm,vmacache: optimize overflow system-wide flushing
X-Git-Tag: next-20140530~2^2~376
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e7785c2fa049c9f40a743f231513d8475b96441c;p=karo-tx-linux.git

mm,vmacache: optimize overflow system-wide flushing

For single threaded workloads, we can avoid flushing and iterating through
the entire list of tasks, making the whole function a lot faster,
requiring only a single atomic read for the mm_users.

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/vmacache.c b/mm/vmacache.c
index 658ed3b3e38d..9f25af825dec 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -17,6 +17,16 @@ void vmacache_flush_all(struct mm_struct *mm)
 {
 	struct task_struct *g, *p;
 
+	/*
+	 * Single threaded tasks need not iterate the entire
+	 * list of process. We can avoid the flushing as well
+	 * since the mm's seqnum was increased and don't have
+	 * to worry about other threads' seqnum. Current's
+	 * flush will occur upon the next lookup.
+	 */
+	if (atomic_read(&mm->mm_users) == 1)
+		return;
+
 	rcu_read_lock();
 	for_each_process_thread(g, p) {
 		/*