This issue is common to every SSD, DRAM or DRAM-less doesn't matter, as mentioned before
What I do is create partition using only 90% of total space, so 10% remains unallocated. So I don't need to keep track of free space, and even if I fill up the partition, the disk itself is never full so speed never drops. Also the unallocated space can be used by the controller for wear levelling as required
