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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmacache.c b/mm/vmacache.c
index 658ed3b..9f25af8 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -17,6 +17,16 @@
{
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) {
/*