Re: [PATCH 06/17] Btrfs: introduce grab/put functions for the root of the fs/file tree

[Miao Xie <miaox@cn.fujitsu.com>]

On 	thu, 16 May 2013 22:57:07 +0800, Liu Bo wrote:
> On Thu, May 16, 2013 at 10:34:55AM -0400, Chris Mason wrote:
>> Quoting Liu Bo (2013-05-16 10:31:39)
>>> On Thu, May 16, 2013 at 07:54:17AM -0400, Chris Mason wrote:
>>>> Quoting Miao Xie (2013-05-16 03:22:37)
>>>>>> I must say that the patch itself looks harmless, the reason is not good enough.
>>>>>
>>>>> I don't agree with you.
>>>>> It is perishing that The memory reclaim task is blocked for a long time. We should avoid
>>>>> this problem.
>>>>
>>>> synchronize_rcu and friends can take a very very long time.  I like this
>>>> patch as a way to avoid them, it's just keeps the whole kernel moving.
>>>>
>>>> -chris
>>>
>>> Okay, that teaches me another lesson, thanks Miao :)
>>
>> Actually using the rcu api isn't a huge impact.  It's just the
>> synchronize_rcu variants that should be avoided ;)
>>
>> -chris
>>
> 
> Now that it's so slow, I wonder why not use call_srcu() instead?

I have considered this approach, but there is a problem that someone may insert
a new inode after we call call_srcu(). So I had to make this patch as a interim
solution. My next work is to remove synchronize_srcu() from tree_del_inode().

Thanks
Miao