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Re: [PATCH 2/2] xfs: recovery of swap extents operations for CRC filesys

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 2/2] xfs: recovery of swap extents operations for CRC filesystems
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Mon, 09 Sep 2013 15:37:58 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1377822225-17621-3-git-send-email-david@xxxxxxxxxxxxx>
References: <1377822225-17621-1-git-send-email-david@xxxxxxxxxxxxx> <1377822225-17621-3-git-send-email-david@xxxxxxxxxxxxx>
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On 08/29/13 19:23, Dave Chinner wrote:
From: Dave Chinner<dchinner@xxxxxxxxxx>

This is the recovery side of the btree block owner change operation
performed by swapext on CRC enabled filesystems. We detect that an
owner change is needed by the flag that has been placed on the inode
log format flag field. Because the inode recovery is being replayed
after the buffers that make up the BMBT in the given checkpoint, we
can walk all the buffers and directly modify them when we see the
flag set on an inode.

Because the inode can be relogged and hence present in multiple
chekpoints with the "change owner" flag set, we could do multiple
passes across the inode to do this change. While this isn't optimal,
we can't directly ignore the flag as there may be multiple
independent swap extent operations being replayed on the same inode
in different checkpoints so we can't ignore them.

Further, because the owner change operation uses ordered buffers, we
might have buffers that are newer on disk than the current
checkpoint and so already have the owner changed in them. Hence we
cannot just peek at a buffer in the tree and check that it has the
correct owner and assume that the change was completed.

So, for the moment just brute force the owner change every time we
see an inode with the flag set. Note that we have to be careful here
because the owner of the buffers may point to either the old owner
or the new owner. Currently the verifier can't verify the owner
directly, so there is no failure case here right now. If we verify
the owner exactly in future, then we'll have to take this into
account.


...


Recovery of swap extent makes sense. Variable name, XFS_ILOG_DOWNER, gave me a chuckle but it is consistent with the other names.

Really could use some recovery test for this. Did inode create recovery get a test?

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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