Re: [PATCH] Btrfs: keep dropped roots in cache until transaciton commit

From: Josef Bacik <jbacik@fb.com>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>,
	<linux-btrfs@vger.kernel.org>, <kernel-team@fb.com>,
	<mfasheh@suse.de>
Subject: Re: [PATCH] Btrfs: keep dropped roots in cache until transaciton commit
Date: Fri, 11 Sep 2015 11:44:08 -0400	[thread overview]
Message-ID: <55F2F6C8.60307@fb.com> (raw)
In-Reply-To: <55F22D8D.6090406@cn.fujitsu.com>

On 09/10/2015 09:25 PM, Qu Wenruo wrote:
>
>
> Josef Bacik wrote on 2015/09/10 16:27 -0400:
>> When dropping a snapshot we need to account for the qgroup changes.
>> If we drop
>> the snapshot in all one go then the backref code will fail to find
>> blocks from
>> the snapshot we dropped since it won't be able to find the root in the
>> fs root
>> cache.  This can lead to us failing to find refs from other roots that
>> pointed
>> at blocks in the now deleted root.  To handle this we need to not
>> remove the fs
>> roots from the cache until after we process the qgroup operations.  Do
>> this by
>> adding dropped roots to a list on the transaction, and letting the
>> transaction
>> remove the roots at the same time it drops the commit roots.  This
>> will keep all
>> of the backref searching code in sync properly, and fixes a problem
>> Mark was
>> seeing with snapshot delete and qgroups.  Thanks,Btrfs: keep dropped
>> roots in
>> cache until transaciton commit
>>
>> When dropping a snapshot we need to account for the qgroup changes.
>> If we drop
>> the snapshot in all one go then the backref code will fail to find
>> blocks from
>> the snapshot we dropped since it won't be able to find the root in the
>> fs root
>> cache.  This can lead to us failing to find refs from other roots that
>> pointed
>> at blocks in the now deleted root.  To handle this we need to not
>> remove the fs
>> roots from the cache until after we process the qgroup operations.  Do
>> this by
>> adding dropped roots to a list on the transaction, and letting the
>> transaction
>> remove the roots at the same time it drops the commit roots.  This
>> will keep all
>> of the backref searching code in sync properly, and fixes a problem
>> Mark was
>> seeing with snapshot delete and qgroups.  Thanks,
>
> Mark will definitely be happy with this patch, as quite a good basis for
> snapshot deletion.
>
> BTW, the commit message seems to be repeating itself.
>

Argh I usually notice when that happens, there's some weird vim key 
combo that I accidently hit pretty regularly that duplicates everything 
I just typed.  Thanks,

Josef