Re: [RFC 1/3] xfs: Re-introduce xg_active_wq field in struct xfs_group

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

On Thu, Jul 17, 2025 at 04:00:43PM +0530, Nirjhar Roy (IBM) wrote:
> pag_active_wq was removed in
> commit 9943b4573290
> 	("xfs: remove the unused pag_active_wq field in struct xfs_perag")
> because it was not waited upon. Re-introducing this in struct xfs_group.
> This patch also replaces atomic_dec() in xfs_group_rele() with
> 
> if (atomic_dec_and_test(&xg->xg_active_ref))
> 	wake_up(&xg->xg_active_wq);
> 
> The reason for this change is that the online shrink code will wait
> for all the active references to come down to zero before actually
> starting the shrink process (only if the number of blocks that
> we are trying to remove is worth 1 or more AGs).

...and I guess this is the start of being able to remove live rtgroups
too?

> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_group.c | 4 +++-
>  fs/xfs/libxfs/xfs_group.h | 1 +
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_group.c b/fs/xfs/libxfs/xfs_group.c
> index e9d76bcdc820..1fe5319de338 100644
> --- a/fs/xfs/libxfs/xfs_group.c
> +++ b/fs/xfs/libxfs/xfs_group.c
> @@ -147,7 +147,8 @@ xfs_group_rele(
>  	struct xfs_group	*xg)
>  {
>  	trace_xfs_group_rele(xg, _RET_IP_);
> -	atomic_dec(&xg->xg_active_ref);
> +	if (atomic_dec_and_test(&xg->xg_active_ref))
> +		wake_up(&xg->xg_active_wq);
>  }
>  
>  void
> @@ -198,6 +199,7 @@ xfs_group_insert(
>  	xfs_defer_drain_init(&xg->xg_intents_drain);
>  
>  	/* Active ref owned by mount indicates group is online. */
> +	init_waitqueue_head(&xg->xg_active_wq);
>  	atomic_set(&xg->xg_active_ref, 1);
>  
>  	error = xa_insert(&mp->m_groups[type].xa, index, xg, GFP_KERNEL);
> diff --git a/fs/xfs/libxfs/xfs_group.h b/fs/xfs/libxfs/xfs_group.h
> index 4423932a2313..dbef389ef838 100644
> --- a/fs/xfs/libxfs/xfs_group.h
> +++ b/fs/xfs/libxfs/xfs_group.h
> @@ -11,6 +11,7 @@ struct xfs_group {
>  	enum xfs_group_type	xg_type;
>  	atomic_t		xg_ref;		/* passive reference count */
>  	atomic_t		xg_active_ref;	/* active reference count */
> +	wait_queue_head_t xg_active_wq; /* woken active_ref falls to zero */

Nit: tab between the     ^ variable and its type.

With that fixed,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

>  
>  	/* Precalculated geometry info */
>  	uint32_t		xg_block_count;	/* max usable gbno */
> -- 
> 2.43.5
> 
>