Re: [PATCH 6/7] xfs: don't update file system geometry through transaction deltas

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

On Fri, Oct 11, 2024 at 09:59:03AM +0200, Christoph Hellwig wrote:
> On Thu, Oct 10, 2024 at 12:01:47PM -0700, Darrick J. Wong wrote:
> > What if instead this took the form of a new defer_ops type?  The
> > xfs_prepare_sb_update function would allocate a tracking object where
> > we'd pin the sb buffer and record which fields get changed, as well as
> > the new values.  xfs_commit_sb_update then xfs_defer_add()s it to the
> > transaction and commits it.  (The ->create_intent function would return
> > NULL so that no log item is created.)
> > 
> > The ->finish_item function would then bhold the sb buffer, update the
> > ondisk super like how xfs_commit_sb_update does in this patch, set
> > XFS_SB_TRANS_SYNC, and return -EAGAIN.  The defer ops would commit and
> > flush that transaction and call ->finish_item again, at which point it
> > would recompute the incore/cached geometry as necessary, bwrite the sb
> > buffer, and release it.
> > 
> > The downside is that it's more complexity, but the upside is that the
> > geometry changes are contained in one place instead of being scattered
> > around, and the incore changes only happen if the synchronous
> > transaction actually gets written to disk.  IOWs, the end result is the
> > same as what you propose here, but structured differently.  
> 
> That sounds overkill at first, but if we want to move all sb updates
> to that model more strutured infrastructure might be very useful.

<nod> We could just take this as-is and refactor it into the defer item
code once we're done making all the other sb geometry growfsrt updates.
I'd rather do that than rebase *two* entire patchsets just to get the
same results.

--D