On Fri, Aug 24, 2012 at 02:51:51PM -0700, Andrew Morton wrote:
>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.
>
Yes, we can perform sleeping while allocating memory, but we're holding
the "mmap_sem". GFP_KERNEL possiblly block somebody else who also waits
on mmap_sem for long time even though the case should be rare :-)
Thanks,
Gavin
>> + 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);
>>
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>