> [ENHANCEMENT]
> This patch will introduce btrfs_device::hint_free_dev_extent member to
> give some hint for chunk allocator to find free dev extents.
>
> The hint itself is pretty simple, only tells where the first free slot
> could possibly be.
>
> It is not 100% correct, unlike free space cac
[PROBLEM]
When allocating a 4G file, falloc() call is slower and slower if the fs
is more and more filled.
This is going to be super obvious when doing some crazy test.
E.g. fallocating a 1PiB file TiB by TiB.
The first 16T only takes 10 seconds to finish while the last 16TiB can
take over 15min t
