On Fri, 24 Aug 2012 22:37:55 +0800
Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> wrote:
> From: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
>
> 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 cause some overhead. The patch tries to
> eleminate that.
>
> Signed-off-by: Gavin Shan <shangw@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx>
> ---
> mm/mmu_notifier.c | 22 +++++++++++-----------
> 1 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 862b608..fb4067f 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -192,22 +192,23 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
>
> BUG_ON(atomic_read(&mm->mm_users) <= 0);
>
> - 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_ATOMIC);
Why was the code switched to the far weaker GFP_ATOMIC? We can still
perform sleeping allocations inside mmap_sem.
> + 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);
>
--
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