mm/mmu_notifier: init notifier if necessary (e0f3c3f7) · Commits · 戴 / test

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>

mm/mmu_notifier.c

+11 −11

Original line number	Diff line number	Diff line
		@@ -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;
		}

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