The _field_info_collate_fields() memory usage issue has a D7 patch that brings massive performance enhancements, by implementing more granular loading of field and field instance definitions.
The exact impact depends on the number of entity types, bundles and fields. An an example, a core setup with 10 node types, 50 fields on each node type sees:
- frontpage with 10 nodes: -5% CPU, -25% MemUse
- node/%nid: -22% CPU, -60% MemUse
That's a bare core install, with a fairly large number of fields. Numbers on an actual site, with additional contrib modules taking part in the page generation, will probably be lower - still the improvements should be quite noticeable.
Special care was given to ensure that the changes maintain strict API compatibility.
However, as David Rothstein states, "this is one of the bigger and more far-reaching patches we're ever going to commit to D7". D7 maintainers would feel more comfortable committing this with a confirmation from the community that the patch does not break anything on some real-life, real-size sites.
I'm specifically thinking of large drupal distros or products: Acquia Gardens, Commerce Kickstart, OpenPublish, OpenPublic, Panopoly...
Just apply the patch, clear caches, and check that the site still works :-) (extra bonus points for products with a test suite of their own...)
Next "D7 bugfix release" window is Feb 2nd. Let's get this in !