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 <shangw@linux.vnet.ibm.com>
Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Sagi Grimberg <sagig@mellanox.co.il>
Cc: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 11 deletions

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 35ff447d8d1..947df83dccb 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -207,22 +207,23 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
         */
         BUG_ON(!srcu.per_cpu_ref);
 
-        ret = -ENOMEM;
-        mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
-        if (unlikely(!mmu_notifier_mm))
-                goto out;
-
         if (take_mmap_sem)
                 down_write(&mm->mmap_sem);
         ret = mm_take_all_locks(mm);
         if (unlikely(ret))
-                goto out_cleanup;
+                goto out;
 
         if (!mm_has_notifiers(mm)) {
+                mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm),
+                                        GFP_KERNEL);
+                if (unlikely(!mmu_notifier_mm)) {
+                        ret = -ENOMEM;
+                        goto out_of_mem;
+                }
                 INIT_HLIST_HEAD(&mmu_notifier_mm->list);
                 spin_lock_init(&mmu_notifier_mm->lock);
+
                 mm->mmu_notifier_mm = mmu_notifier_mm;
-                mmu_notifier_mm = NULL;
         }
         atomic_inc(&mm->mm_count);
 
@@ -238,13 +239,12 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
         hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
         spin_unlock(&mm->mmu_notifier_mm->lock);
 
+out_of_mem:
         mm_drop_all_locks(mm);
-out_cleanup:
+out:
         if (take_mmap_sem)
                 up_write(&mm->mmap_sem);
-        /* kfree() does nothing if mmu_notifier_mm is NULL */
-        kfree(mmu_notifier_mm);
-out:
+
         BUG_ON(atomic_read(&mm->mm_users) <= 0);
         return ret;
 }