Re: [PATCH v4 4/6] xfs: generic AG set based steering

[Christoph Hellwig <hch@lst.de>]

On Fri, Jul 17, 2026 at 06:25:36PM +0530, Kanchan Joshi wrote:
> Improve allocator concurrency and reduce interleaving by introducing
> fixed sized AG set.
> Use low bits of the inode as a hash to select AG within the AG set.
> Overall, a file will try to use the same AG (and contiguity is maintained),
> but multiple files will be spread across all AGs in the target AG set.

I'm a bit worried this kind of magic - the inodes close to each other
might not all have data or very different amounts of data.

I suspect the root cause this helps with is that the XFS initial data
placement algorithm that tries to place file data next to the inode is
actively harmful these days.  So doing an initial AG selection similar
to how the RT device does the initial RTG selection might be more
useful here (and thinking about moving to an inode32-like scheme
where small metadata with a lot of churn is constrained to a few
AGs).