Re: [PATCH 8/8] xfs: factor inode lookup from xfs_ifree_cluster

[Brian Foster <bfoster@redhat.com>]

On Wed, Mar 25, 2020 at 12:42:05PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> There's lots of indent in this code which makes it a bit hard to
> follow. We are also going to completely rework the inode lookup code
> as part of the inode reclaim rework, so factor out the inode lookup
> code from the inode cluster freeing code.
> 
> Based on prototype code from Christoph Hellwig.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---

https://lore.kernel.org/linux-xfs/20191104232000.GR4153244@magnolia/
https://lore.kernel.org/linux-xfs/20191101120521.GE59146@bfoster/

>  fs/xfs/xfs_inode.c | 152 +++++++++++++++++++++++++--------------------
>  1 file changed, 84 insertions(+), 68 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 14b922f2a6db7..5c930863ed5b8 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2503,6 +2503,88 @@ xfs_iunlink_remove(
>  	return error;
>  }
>  
> +/*
> + * Look up the inode number specified and mark it stale if it is found. If it is
> + * dirty, return the inode so it can be attached to the cluster buffer so it can
> + * be processed appropriately when the cluster free transaction completes.
> + */
> +static struct xfs_inode *
> +xfs_ifree_get_one_inode(
> +	struct xfs_perag	*pag,
> +	struct xfs_inode	*free_ip,
> +	int			inum)
> +{
> +	struct xfs_mount	*mp = pag->pag_mount;
> +	struct xfs_inode	*ip;
> +
> +retry:
> +	rcu_read_lock();
> +	ip = radix_tree_lookup(&pag->pag_ici_root, XFS_INO_TO_AGINO(mp, inum));
> +
> +	/* Inode not in memory, nothing to do */
> +	if (!ip)
> +		goto out_rcu_unlock;
> +
> +	/*
> +	 * because this is an RCU protected lookup, we could find a recently
> +	 * freed or even reallocated inode during the lookup. We need to check
> +	 * under the i_flags_lock for a valid inode here. Skip it if it is not
> +	 * valid, the wrong inode or stale.
> +	 */
> +	spin_lock(&ip->i_flags_lock);
> +	if (ip->i_ino != inum || __xfs_iflags_test(ip, XFS_ISTALE)) {
> +		spin_unlock(&ip->i_flags_lock);
> +		goto out_rcu_unlock;
> +	}
> +	spin_unlock(&ip->i_flags_lock);
> +
> +	/*
> +	 * Don't try to lock/unlock the current inode, but we _cannot_ skip the
> +	 * other inodes that we did not find in the list attached to the buffer
> +	 * and are not already marked stale. If we can't lock it, back off and
> +	 * retry.
> +	 */
> +	if (ip != free_ip) {
> +		if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
> +			rcu_read_unlock();
> +			delay(1);
> +			goto retry;
> +		}
> +
> +		/*
> +		 * Check the inode number again in case we're racing with
> +		 * freeing in xfs_reclaim_inode().  See the comments in that
> +		 * function for more information as to why the initial check is
> +		 * not sufficient.
> +		 */
> +		if (ip->i_ino != inum) {
> +			xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +			goto out_rcu_unlock;
> +		}
> +	}
> +	rcu_read_unlock();
> +
> +	xfs_iflock(ip);
> +	xfs_iflags_set(ip, XFS_ISTALE);
> +
> +	/*
> +	 * We don't need to attach clean inodes or those only with unlogged
> +	 * changes (which we throw away, anyway).
> +	 */
> +	if (!ip->i_itemp || xfs_inode_clean(ip)) {
> +		ASSERT(ip != free_ip);
> +		xfs_ifunlock(ip);
> +		xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +		goto out_no_inode;
> +	}
> +	return ip;
> +
> +out_rcu_unlock:
> +	rcu_read_unlock();
> +out_no_inode:
> +	return NULL;
> +}
> +
>  /*
>   * A big issue when freeing the inode cluster is that we _cannot_ skip any
>   * inodes that are in memory - they all must be marked stale and attached to
> @@ -2603,77 +2685,11 @@ xfs_ifree_cluster(
>  		 * even trying to lock them.
>  		 */
>  		for (i = 0; i < igeo->inodes_per_cluster; i++) {
> -retry:
> -			rcu_read_lock();
> -			ip = radix_tree_lookup(&pag->pag_ici_root,
> -					XFS_INO_TO_AGINO(mp, (inum + i)));
> -
> -			/* Inode not in memory, nothing to do */
> -			if (!ip) {
> -				rcu_read_unlock();
> +			ip = xfs_ifree_get_one_inode(pag, free_ip, inum + i);
> +			if (!ip)
>  				continue;
> -			}
> -
> -			/*
> -			 * because this is an RCU protected lookup, we could
> -			 * find a recently freed or even reallocated inode
> -			 * during the lookup. We need to check under the
> -			 * i_flags_lock for a valid inode here. Skip it if it
> -			 * is not valid, the wrong inode or stale.
> -			 */
> -			spin_lock(&ip->i_flags_lock);
> -			if (ip->i_ino != inum + i ||
> -			    __xfs_iflags_test(ip, XFS_ISTALE)) {
> -				spin_unlock(&ip->i_flags_lock);
> -				rcu_read_unlock();
> -				continue;
> -			}
> -			spin_unlock(&ip->i_flags_lock);
> -
> -			/*
> -			 * Don't try to lock/unlock the current inode, but we
> -			 * _cannot_ skip the other inodes that we did not find
> -			 * in the list attached to the buffer and are not
> -			 * already marked stale. If we can't lock it, back off
> -			 * and retry.
> -			 */
> -			if (ip != free_ip) {
> -				if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
> -					rcu_read_unlock();
> -					delay(1);
> -					goto retry;
> -				}
> -
> -				/*
> -				 * Check the inode number again in case we're
> -				 * racing with freeing in xfs_reclaim_inode().
> -				 * See the comments in that function for more
> -				 * information as to why the initial check is
> -				 * not sufficient.
> -				 */
> -				if (ip->i_ino != inum + i) {
> -					xfs_iunlock(ip, XFS_ILOCK_EXCL);
> -					rcu_read_unlock();
> -					continue;
> -				}
> -			}
> -			rcu_read_unlock();
>  
> -			xfs_iflock(ip);
> -			xfs_iflags_set(ip, XFS_ISTALE);
> -
> -			/*
> -			 * we don't need to attach clean inodes or those only
> -			 * with unlogged changes (which we throw away, anyway).
> -			 */
>  			iip = ip->i_itemp;
> -			if (!iip || xfs_inode_clean(ip)) {
> -				ASSERT(ip != free_ip);
> -				xfs_ifunlock(ip);
> -				xfs_iunlock(ip, XFS_ILOCK_EXCL);
> -				continue;
> -			}
> -
>  			iip->ili_last_fields = iip->ili_fields;
>  			iip->ili_fields = 0;
>  			iip->ili_fsync_fields = 0;
> -- 
> 2.26.0.rc2
>