ORLANDO — General managers across the baseball landscape are filing into the Waldorf Astoria for the annual GM meetings, where officials gather to lay groundwork for future player movement and every so often pull off a deal before departing.

Much of the Giants’ contingent arrived Sunday, including GM Bobby Evans, while Billy Beane and David Forst of the A’s arrived Monday morning.

The meetings last through Wednesday, and owners will meet here Wednesday and Thursday.

This figures to be the Giants’ busiest and most intense offseason in recent history because of their high payroll and massive holes on their roster, which they’re trying to get younger and more athletic. The Giants need two outfielders, a third baseman and plenty of bullpen help.

I was told the Giants have checked in on free-agent reliever Brandon Morrow, who’s coming off a spectacular season as a Dodgers setup man. The Giants need an upgraded surrounding cast for closer Mark Melancon, who had a forgettable first year in San Francisco.

Many teams are calling on Morrow, who played at Rancho Cotate High School in Rohnert Park and Cal, though he has expressed his desire to return to Los Angeles.

Similarly, I was just told free-agent reliever Joe Smith, who finished last season in Cleveland, is receiving ample interest from teams as bullpens have become more highly used and valued industry-wide.

It’s a deep crop of free-agent relievers including Addison Reed, Anthony Swarzak, Brandon Kintzler, Steve Cishek, Tony Watson, Bryan Shaw, Juan Nicasio and Mike Minor along with closers Wade Davis and Greg Holland.

John Shea is The San Francisco Chronicle’s national baseball writer. Email: jshea@sfchronicle.com Twitter: @JohnSheaHey