Re: [PATCH 3/9] xfs: convert buffer cache to use high order folios

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Mar 21, 2024 at 02:28:23PM -0700, Christoph Hellwig wrote:
> On Wed, Mar 20, 2024 at 07:40:05PM -0700, Darrick J. Wong wrote:
> > > Well xfs_verity.c could just zlib/zstd/whatever compress the contents
> > > and see if that helps.  We only need a ~2% compression to shrink to a
> > > single 4k block, a ~1% reduction for 64k blocks, or a 6% reduction for
> > > 1k blocks.
> > 
> > ...or we just turn off the attr remote header for XFS_ATTR_VERITY merkle
> > tree block values and XOR i_ino, merkle_pos, and the fs uuid into the
> > first 32 bytes.
> 
> That does sound much better than wasting the space or crazy compression
> schemes.

It turns out that merkle tree blocks are nearly "random" data, which
means that my experiments with creating fsverity files and trying to
compress merkle tree blocks actually made it *bigger*.  No zlib for us!

--D