From: Chris Mason <chris.mason@oracle.com>
To: Yan Zheng <yanzheng@21cn.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Algorithm for nodatacow is broken
Date: Wed, 16 Jul 2008 13:15:54 +0000 [thread overview]
Message-ID: <1216214154.24425.326.camel@think.oraclecorp.com> (raw)
In-Reply-To: <3d0408630807160041h20d2157agfc221b34a836df87@mail.gmail.com>
On Wed, 2008-07-16 at 15:41 +0800, Yan Zheng wrote:
> Hello,
>
> Yesterday, I realized the algorithm for nodatacow is broken, it can't
> reliably detect whether a given extent is referenced by only one
> snapshot.
I had to change around nodatacow back in May because it was definitely
broken in the way you describe. I agree the special case I added to
allow nodatacow when one of the references comes from the running
transaction is broken.
But, we should be able to fix it by extending the reference count checks
up the tree. Any reference > 1 not held by the running transaction on
any block should force a cow.
-chris
next prev parent reply other threads:[~2008-07-16 13:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-07-16 7:41 Algorithm for nodatacow is broken Yan Zheng
2008-07-16 13:15 ` Chris Mason [this message]
2008-07-17 12:45 ` Chris Mason
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