Says here that Mac OS 10.10.4 introduces a command-line TRIM enablement for third-party SSDs:

https://github.com/Temptin/Documents/blob/master/OSX_TRIM_Tutorial.md

Another article on the subject:

http://www.macrumors.com/2015/07/01/os-x-trim-ssd/

There is some trepidation as to the safety of this feature on some SSDs (Samsung and Crucial, mostly), but this article says that it should be safe to run on a Samsung drive because of OSX's using sequential rather than queued TRIMming:

http://forums.macrumors.com/threads...ved-performance.1891936/page-10#post-21469307

I just ran "sudo trimforce enable" in Terminal, and my Macbook Pro re-booted. (I also have my Samsung 840 SSD backed-up, just in case.) System Info reads "TRIM Support: Yes."

Surely others will have things to add to this; I just thought it was cool of Apple to finally give up the TRIM.

 

However if your SSD is a slightly older model using the Command Line TrimForce might break your MacOSX 10.10.4 as it did mine. It would not boot after restart and showed a grey circle with a diagonal line through it. The safe way to enable Trim in Yosemite with older SSDs is to use the latest version of Disk Sensei v1.2. You can download the demo version and register it with Paddle Generic KeyfileGen v2.2 CORE.

 

or you can use Trim Enabler