Inactive Memory

Description

Some Mac OS X users have reported that when they run Transmission, their system's Activity Monitor shows their Free memory keeps shrinking and their Inactive Memory keeps growing. This is sometimes mistaken as a memory leak, but is actually Mac OS X's normal behavior. As this ​support.apple.com article explains, Inactive memory is not actually in use by Transmission and is recycled by the Mac OS X memory manager when other applications need it:

"This means you shouldn't worry when the Free memory is low. The only time Free memory should be high is right after the computer starts up. As you use applications or services, memory is used and transitions to Inactive. Applications that need more memory will take from the Inactive, but the Inactive is there just in case you need it again. If the combination of Free and Inactive is very low, then you might need more memory."