After this article was written, `free -m` on many systems started to have an "available" column that shows the sum of reclaimable and free memory. It's nicer than the "-/+" section shown in this old article.

  $ free -m
                 total        used        free      shared  buff/cache   available
  Mem:            3915        2116        1288          41         769        1799
  Swap:            974           0         974