Re: [PATCH 2/2] ceph: do not release the global snaprealm until unmounting

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-02-22 at 14:34 +0800, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> The global snaprealm would be created and then destroyed immediately
> every time when updating it.
> 

Does this cause some sort of issue, or is it just inefficient?

> URL: https://tracker.ceph.com/issues/54362
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>  fs/ceph/mds_client.c         |  2 +-
>  fs/ceph/snap.c               | 13 +++++++++++--
>  fs/ceph/super.h              |  2 +-
>  include/linux/ceph/ceph_fs.h |  3 ++-
>  4 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 65bd43d4cafc..325f8071a324 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -4866,7 +4866,7 @@ void ceph_mdsc_close_sessions(struct ceph_mds_client *mdsc)
>  	mutex_unlock(&mdsc->mutex);
>  
>  	ceph_cleanup_snapid_map(mdsc);
> -	ceph_cleanup_empty_realms(mdsc);
> +        ceph_cleanup_global_and_empty_realms(mdsc);

Please use tab indent.

>  
>  	cancel_work_sync(&mdsc->cap_reclaim_work);
>  	cancel_delayed_work_sync(&mdsc->delayed_work); /* cancel timer */
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index 66a1a92cf579..cc9097c27052 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -121,7 +121,11 @@ static struct ceph_snap_realm *ceph_create_snap_realm(
>  	if (!realm)
>  		return ERR_PTR(-ENOMEM);
>  
> -	atomic_set(&realm->nref, 1);    /* for caller */
> +	/* Do not release the global dummy snaprealm until unmouting */
> +	if (ino == CEPH_INO_GLOBAL_SNAPREALM)
> +		atomic_set(&realm->nref, 2);
> +	else
> +		atomic_set(&realm->nref, 1);
>  	realm->ino = ino;
>  	INIT_LIST_HEAD(&realm->children);
>  	INIT_LIST_HEAD(&realm->child_item);
> @@ -261,9 +265,14 @@ static void __cleanup_empty_realms(struct ceph_mds_client *mdsc)
>  	spin_unlock(&mdsc->snap_empty_lock);
>  }
>  
> -void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc)
> +void ceph_cleanup_global_and_empty_realms(struct ceph_mds_client *mdsc)
>  {
> +	struct ceph_snap_realm *global_realm;
> +
>  	down_write(&mdsc->snap_rwsem);
> +	global_realm = __lookup_snap_realm(mdsc, CEPH_INO_GLOBAL_SNAPREALM);
> +	if (global_realm)
> +		ceph_put_snap_realm(mdsc, global_realm);
>  	__cleanup_empty_realms(mdsc);
>  	up_write(&mdsc->snap_rwsem);
>  }
> diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> index baac800a6d11..250aefecd628 100644
> --- a/fs/ceph/super.h
> +++ b/fs/ceph/super.h
> @@ -942,7 +942,7 @@ extern void ceph_handle_snap(struct ceph_mds_client *mdsc,
>  			     struct ceph_msg *msg);
>  extern int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
>  				  struct ceph_cap_snap *capsnap);
> -extern void ceph_cleanup_empty_realms(struct ceph_mds_client *mdsc);
> +extern void ceph_cleanup_global_and_empty_realms(struct ceph_mds_client *mdsc);
>  
>  extern struct ceph_snapid_map *ceph_get_snapid_map(struct ceph_mds_client *mdsc,
>  						   u64 snap);
> diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
> index f14f9bc290e6..86bf82dbd8b8 100644
> --- a/include/linux/ceph/ceph_fs.h
> +++ b/include/linux/ceph/ceph_fs.h
> @@ -28,7 +28,8 @@
>  
>  
>  #define CEPH_INO_ROOT   1
> -#define CEPH_INO_CEPH   2       /* hidden .ceph dir */
> +#define CEPH_INO_CEPH   2            /* hidden .ceph dir */
> +#define CEPH_INO_GLOBAL_SNAPREALM  3 /* global dummy snaprealm */
>  
>  /* arbitrary limit on max # of monitors (cluster of 3 is typical) */
>  #define CEPH_MAX_MON   31
-- 
Jeff Layton <jlayton@kernel.org>