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Juergen Gross
8bf435cdf2
Today all Xenstore nodes are stored in a TDB data base. This data base has several disadvantages: - It is using a fixed sized hash table, resulting in high memory overhead for small installations with only very few VMs, and a rather large performance hit for systems with lots of VMs due to many collisions. The hash table size today is 7919 entries. This means that e.g. in case of a simple desktop use case with 2 or 3 VMs probably far less than 10% of the entries will be used (assuming roughly 100 nodes per VM). OTOH a setup on a large server with 500 VMs would result in heavy conflicts in the hash list with 5-10 nodes per hash table entry. - TDB is using a single large memory area for storing the nodes. It only ever increases this area and will never shrink it afterwards. This will result in more memory usage than necessary after a peak of Xenstore usage. - Xenstore is only single-threaded, while TDB is designed to be fit for multi-threaded use cases, resulting in much higher code complexity than needed. - Special use cases of Xenstore are not possible to implement with TDB in an effective way, while an implementation of a data base tailored for Xenstore could simplify some handling (e.g. transactions) a lot. So drop using TDB and store the nodes directly in memory making them easily accessible. Use a hash-based lookup mechanism for fast lookup of nodes by their full path. For now only replace TDB keeping the current access functions. Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Julien Grall <jgrall@amazon.com>