[Copied from the original issue:]
During a page rendering sequence we experience numerous DefinitionProvider#get() calls which for the case of YamlDefinitionProvider lead to the last modification date checks for all of the involved files. This adds a tiny performance overhead per call which stacks up into a big one and also is prone to exceed the open file descriptor quota.
Solution here is to perform the last modification checks not more often that 1 per a second (in a normal development case - this is negligible from the dev experience point of view)