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

Source: LWN.net – [$] Issues around discard