Re: [Xen-devel] [PATCH v5 3/4] xenstore: rework of transaction handling

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Mar 31, 2017 at 01:29:19PM +0200, Juergen Gross wrote:
> The handling of transactions in xenstored is rather clumsy today:
> 
> - Each transaction in progress is keeping a local copy of the complete
>   xenstore data base
> - A transaction will fail as soon as any node is being modified outside
>   the transaction
> 
> This is leading to a very bad behavior in case of a large xenstore.
> Memory consumption of xenstored is much higher than necessary and with
> many domains up transactions failures will be more and more common.
> 
> Instead of keeping a complete copy of the data base for each
> transaction store the transaction data in the same data base as the
> normal xenstore entries prepended with the transaction in the single
> nodes either read or modified. At the end of the transaction walk
> through all nodes accessed and check for conflicting modifications.
> In case no conflicts are found write all modified nodes to the data
> base without transaction identifier.
> 
> Following tests have been performed:
> - create/destroy of various domains, including HVM with ioemu-stubdom
>   (xenstored and xenstore-stubdom)
> - multiple concurrent runs of xs-test over several minutes
>   (xenstored and xenstore-stubdom)
> - test for memory leaks of xenstored by dumping talloc reports before
>   and after the tests
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

With the suggestion to update the comment taken care of:

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

Given this is rather complex code it would be helpful to have a second
opinion.

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