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>

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 35ff447..947df83 100644 (file)
--- 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;
 }