mm/mmu_notifier: init notifier if necessary
mm/mmu_notifier: init notifier if necessary

While registering MMU notifier, new instance of MMU notifier_mm will be
allocated and later free'd if currrent mm_struct's MMU notifier_mm has
been initialized.  That causes some overhead.  The patch tries to
elominate that.

Signed-off-by: Gavin Shan <4d6e32db2683aba4a3f3669c68ac02b37d1b91cd@linux.vnet.ibm.com>
Signed-off-by: Wanpeng Li <86d530c4a0b810dc887df1e4e084ed44c9b7acac@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <6cb163d975a8c4c46420677e0054b55c39bdb339@redhat.com>
Cc: Avi Kivity <8f920f22884d6fea9df883843c4a8095a2e5ac6f@redhat.com>
Cc: Hugh Dickins <d3abdf3e2800e6cb849f11b81e6eb50b34d96431@google.com>
Cc: Marcelo Tosatti <958bcd1f4a7a8c36dca09fe3fa9cb5f1483adf51@redhat.com>
Cc: Xiao Guangrong <1e0036c3819c78880ef9e9a8457e99783a5661e3@linux.vnet.ibm.com>
Cc: Sagi Grimberg <380ce2a82d3d08e67ab163b51dc6d30288ad3f13@mellanox.co.il>
Cc: Haggai Eran <a558c0e8c8d9df6f2e5864bc715329bac6a2f11b@mellanox.com>
Signed-off-by: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs