Re: [PATCH v2] Btrfs: do not use extent commit root for sending

[Wang Shilong <wangshilong1991@gmail.com>]

Hello Josef,

> 
> On 01/14/2014 11:26 AM, Wang Shilong wrote:
>> From: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
>> 
>> Now we have kicked off transaction from btrfs send, it is not safe
>> that we use extent commit root to search.
>> 
>> I happended to catch this problem when running sending and snapshot
>> in my desktop.
> 
> I'm confused about this, we are searching a read only snapshot, why isn't looking at the commit root ok?  Thanks,

I sent a patch to remove transaction outsize before.

http://git.kernel.org/cgit/linux/kernel/git/mason/linux-btrfs.git/commit/?h=integration&id=e0cbfccf3d518f1fb6f8e10932a67d75df2a4380

Previously, we can search extent commit root, it is because we are protected by join and end transaction, since this patch, we can not.

A further  question is now we still have to join transaction actually, only the transaction protection range is smaller,  but we may encounter
extent root's lock contention. I don't know which approach is better, the url's patch have been pushed into chris's integration branch before
i realized it would caused other problems.

Maybe a better a approach is to join and end transaction outsize of find_extent_clone(), and then we still can use extent commit
root for sending.^_^

Thanks,
Wang
> 
> Josef