Re: [PATCH 0/6] block atomic writes for XFS

[Christoph Hellwig <hch@lst.de>]

On Wed, Feb 14, 2024 at 10:50:22AM +1100, Dave Chinner wrote:
> The functionality atomic writes need from the filesystem is for
> extent alignment constraints to be applied to all extent
> manipulations, not just allocation.  This is the same functionality
> that DAX based XFS filesystems need to guarantee PMD aligned
> extents.
> 
> IOWs, the required filesystem extent alignment functionality is not
> specific to atomic writes and it is not specific to a particular
> type of storage hardware.
> 
> If we implement the generic extent alignment constraints properly,
> everything else from there is just a matter of configuring the
> filesystem geometry to match the underlying hardware capability.
> mkfs can do that for us, like it already does for RAID storage...

Agreed.

But the one thing making atomic writes odd right now is that it
absolutely is required for operation right now, while for other
features is is somewhere between nice and important to have and not
a deal breaker.

So eithe we need to figure out a somewhat generic and not totally
XFS implementation specific user space interface to do the force
alignment (which this series tries to do).  Or we make atomic
writes like the other features and ensure they still work without
the proper alignment if they suck.  Doing that was my initial
gut feeling, and looking at other approaches just makes me tend
even stronger towards that.



> 
> -Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
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