MIN_WRITE_SZ
if (spc - c->dark_wm < MIN_WRITE_SZ)
return spc - MIN_WRITE_SZ;
BUILD_BUG_ON(MIN_WRITE_SZ & 7);
BUILD_BUG_ON(UBIFS_INO_NODE_SZ < MIN_WRITE_SZ);
BUILD_BUG_ON(UBIFS_DENT_NODE_SZ < MIN_WRITE_SZ);
BUILD_BUG_ON(UBIFS_XENT_NODE_SZ < MIN_WRITE_SZ);
BUILD_BUG_ON(UBIFS_TRUN_NODE_SZ < MIN_WRITE_SZ);
c->dead_wm = ALIGN(MIN_WRITE_SZ, c->min_io_size);