[$] Issues around discard

In a combined filesystem and storage session at the 2019 Linux Storage, Filesystem, and Memory-Management Summit (LSFMM), Dennis Zhou wanted to talkabout discard, which is the process of sending commands(e.g. TRIM) to block devices to indicateblocks that are no longer in use. Discard is a "serious black box", hesaid; it is a third way to interact with a drive, but Linux developers haveno real insight into what its actual effects will be. That can lead toperformance and other problems.