Re: [PATCH 1/7] xfs: pass the exact range to initialize to xfs_initialize_perag

[Brian Foster <bfoster@redhat.com>]

On Mon, Sep 30, 2024 at 06:41:42PM +0200, Christoph Hellwig wrote:
> Currently only the new agcount is passed to xfs_initialize_perag, which
> requires lookups of existing AGs to skip them and complicates error
> handling.  Also pass the previous agcount so that the range that
> xfs_initialize_perag operates on is exactly defined.  That way the
> extra lookups can be avoided, and error handling can clean up the
> exact range from the old count to the last added perag structure.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  fs/xfs/libxfs/xfs_ag.c   | 29 ++++++++---------------------
>  fs/xfs/libxfs/xfs_ag.h   |  5 +++--
>  fs/xfs/xfs_fsops.c       | 18 ++++++++----------
>  fs/xfs/xfs_log_recover.c |  5 +++--
>  fs/xfs/xfs_mount.c       |  4 ++--
>  5 files changed, 24 insertions(+), 37 deletions(-)
> 
...
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index ec766b4bc8537b..6a165ca55da1a8 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -3346,6 +3346,7 @@ xlog_do_recover(
>  	struct xfs_mount	*mp = log->l_mp;
>  	struct xfs_buf		*bp = mp->m_sb_bp;
>  	struct xfs_sb		*sbp = &mp->m_sb;
> +	xfs_agnumber_t		old_agcount = sbp->sb_agcount;
>  	int			error;
>  
>  	trace_xfs_log_recover(log, head_blk, tail_blk);
> @@ -3393,8 +3394,8 @@ xlog_do_recover(
>  	/* re-initialise in-core superblock and geometry structures */
>  	mp->m_features |= xfs_sb_version_to_features(sbp);
>  	xfs_reinit_percpu_counters(mp);
> -	error = xfs_initialize_perag(mp, sbp->sb_agcount, sbp->sb_dblocks,
> -			&mp->m_maxagi);
> +	error = xfs_initialize_perag(mp, old_agcount, sbp->sb_agcount,
> +			sbp->sb_dblocks, &mp->m_maxagi);

I assume this is because the superblock can change across recovery, but
code wise this seems kind of easy to misread into thinking the variable
is the same. I think the whole old/new terminology is kind of clunky for
an interface that is not just for growfs. Maybe it would be more clear
to use start/end terminology for xfs_initialize_perag(), then it's more
straightforward that mount would init the full range whereas growfs
inits a subrange.

A oneliner comment or s/old_agcount/orig_agcount/ wouldn't hurt here
either. Actually if that's the only purpose for this call and if you
already have to sample sb_agcount, maybe just lifting/copying the if
(old_agcount >= new_agcount) check into the caller would make the logic
more self-explanatory. Hm?

Otherwise the logic changes look Ok to me functionally.

Brian

>  	if (error) {
>  		xfs_warn(mp, "Failed post-recovery per-ag init: %d", error);
>  		return error;
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 1fdd79c5bfa04e..6fa7239a4a01b6 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -810,8 +810,8 @@ xfs_mountfs(
>  	/*
>  	 * Allocate and initialize the per-ag data.
>  	 */
> -	error = xfs_initialize_perag(mp, sbp->sb_agcount, mp->m_sb.sb_dblocks,
> -			&mp->m_maxagi);
> +	error = xfs_initialize_perag(mp, 0, sbp->sb_agcount,
> +			mp->m_sb.sb_dblocks, &mp->m_maxagi);
>  	if (error) {
>  		xfs_warn(mp, "Failed per-ag init: %d", error);
>  		goto out_free_dir;
> -- 
> 2.45.2
> 
>