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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>
This commit is contained in:
Gavin Shan 2012-10-08 16:29:26 -07:00 committed by Linus Torvalds
parent 21a92735f6
commit e0f3c3f78d
1 changed files with 11 additions and 11 deletions
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22
mm/mmu_notifier.c
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@ -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;
}