Re: [PATCH] mkfs: use stx_blksize for dev block size by default

[Christoph Hellwig <hch@infradead.org>]

On Fri, Feb 07, 2025 at 11:04:06AM +0100, Daniel Gomez wrote:
> > > performance in the stx_blksize field of the statx data structure. This
> > > change updates the current default 4 KiB block size for all devices
> > > reporting a minimum I/O larger than 4 KiB, opting instead to query for
> > > its advertised minimum I/O value in the statx data struct.
> > 
> > UUuh, no.  Larger block sizes have their use cases, but this will
> > regress performance for a lot (most?) common setups.  A lot of
> > device report fairly high values there, but say increasing the
> 
> Are these devices reporting the correct value?

Who defines what "correct" means to start with?

> As I mentioned in my
> discussion with Darrick, matching the minimum_io_size with the "fs
> fundamental blocksize" actually allows to avoid RMW operations (when
> using the default path in mkfs.xfs and the value reported is within
> boundaries).

At least for buffered I/O it does not remove RMW operations at all,
it just moves them up.

And for plenty devices the min_io size might be set to larger than
LBA size, but the device is still reasonably efficient at handling
smaller I/O (e.g. because it has power loss protection and stages
writes in powerfail protected memory).