Re: [PATCH v2 00/24] ext4: enable block size larger than page size

[Theodore Ts'o]

I've started looking at this patch series and playing with it, and one
thing which is worth noting is that CONFIG_TRANSPARENT_HUGEPAGE needs
to be enabled, or else sb_set_blocksize() will fail for block size >
page size.  This isn't specific to ext4, and maybe I'm missing
something, but apparently this isn't documented.  I had to go digging
through the source code to figure out what was needed.

I wonder if we should have some kind of warning in sb_set_blocksize()
where if there is an attempt to set a blocksize > page size and
transparent hugepages is not configured, we issue a printk_once()
giving a hint to the user that the reason that the mount failed was
because transparent hugepages wasn't enabled at compile time.

It **really** isn't obvious that large block size support and
transparent hugepages are linked.

					- Ted