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Thomas Haller authored
Rework platform object cache to use NMDedupMultiIndex. Already previously, NMPCache used NMMultiIndex and had thus O(1) for most operations. What is new is: - Contrary to NMMultiIndex, NMDedupMultiIndex preserves the order of the cached items. That is crucial to handle routes properly as kernel will replace the first matching route based on network/plen/metric properties. See related bug rh#1337855. Without tracking the order of routes as they are exposed by kernel, we cannot properly maintain the route cache. - All NMPObject instances are now treated immutable, refcounted and get de-duplicated via NMDedupMultiIndex. This allows to have a global NMDedupMultiIndex that can be shared with NMIP4Config and NMRouteManager. It also allows to share the objects themselves. Immutable objects are so much nicer. We can get rid of the update pre-hook callback, which was required previously because we would mutate the object inplace. Now, we can just update the cache, and compare obj_old and obj_new after the fact. - NMMultiIndex was treated as an internal of NMPCache. On the other hand, NMDedupMultiIndex exposes NMDedupMultiHeadEntry, which is basically an object that allows to iterate over all related objects. That means, we can now lookup objects in the cache and give the NMDedupMultiHeadEntry instance to the caller, which then can iterate the list on it's own -- without need for copying anything. Currently, at various places we still create copies of lookup results. That can be improved later. The ability to share NMPObject instances should enable us to significantly improve performance and scale with large number of routes. Of course there is a memory overhead of having an index for each list entry. Each NMPObject may also require an NMDedupMultiEntry, NMDedupMultiHeadEntry, and NMDedupMultiBox item, which are tracked in a GHashTable. Optimally, one NMDedupMultiHeadEntry is the head for multiple objects, and NMDedupMultiBox is able to deduplicate several NMPObjects, so that there is a net saving. Also, each object type has several indexes of type NMPCacheIdType. So, worst case an NMPlatformIP4Route in the platform cache is tracked by 8 NMPCacheIdType indexes, for each we require a NMDedupMultiEntry, plus the shared NMDedupMultiHeadEntry. The NMDedupMultiBox instance is shared between the 8 indexes (and possibly other).
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