The commit 026d0d27c488 (ext4: reduce computation of overhead during resize) reduces the time taken to resize large bigalloc filesystems(reduces 3+ hours to milliseconds for a 64TB FS). This is a good candidate to cherry-pick to stable releases.
Kiselev, Oleg (1): ext4: reduce computation of overhead during resize
fs/ext4/resize.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-)