Hi,
Yes, this refers to swap.
According to the debugging from software R&D, when testing this file system btrfs can only pass if CONFIG_SWAP is enabled; if CONFIG_SWAP is not enabled, there will be many problems with btrfs.
Once CONFIG_SWAP is enabled, when the physical RAM is full, swap will be used from flash, which may reduce the life of the flash.
Combined with the evaluation with hardware R&D, this file system would not be supported in standard firmware for now. Sorry.