Re: [PATCH 03/16] xfs: detach dquots from inode if we don't need to inactivate it

[Brian Foster <bfoster@redhat.com>]

On Sun, Jun 13, 2021 at 10:20:13AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> If we don't need to inactivate an inode, we can detach the dquots and
> move on to reclamation.  This isn't strictly required here; it's a
> preparation patch for deferred inactivation.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---

Seems functional, but a little more explanation on why we're doing this
might be helpful. Otherwise it's not really clear why we'd duplicate a
bunch of this logic (as opposed to refactor it), if we want to leave
around the obvious maintenance landmine, etc..?

Brian

>  fs/xfs/xfs_icache.c |    8 +++++++-
>  fs/xfs/xfs_inode.c  |   53 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_inode.h  |    2 ++
>  3 files changed, 62 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> index a2d81331867b..7939eced3a47 100644
> --- a/fs/xfs/xfs_icache.c
> +++ b/fs/xfs/xfs_icache.c
> @@ -338,8 +338,14 @@ xfs_inode_mark_reclaimable(
>  {
>  	struct xfs_mount	*mp = ip->i_mount;
>  	struct xfs_perag	*pag;
> +	bool			need_inactive = xfs_inode_needs_inactive(ip);
>  
> -	xfs_inactive(ip);
> +	if (!need_inactive) {
> +		/* Going straight to reclaim, so drop the dquots. */
> +		xfs_qm_dqdetach(ip);
> +	} else {
> +		xfs_inactive(ip);
> +	}
>  
>  	if (!XFS_FORCED_SHUTDOWN(mp) && ip->i_delayed_blks) {
>  		xfs_check_delalloc(ip, XFS_DATA_FORK);
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 3bee1cd20072..85b2b11b5217 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1654,6 +1654,59 @@ xfs_inactive_ifree(
>  	return 0;
>  }
>  
> +/*
> + * Returns true if we need to update the on-disk metadata before we can free
> + * the memory used by this inode.  Updates include freeing post-eof
> + * preallocations; freeing COW staging extents; and marking the inode free in
> + * the inobt if it is on the unlinked list.
> + */
> +bool
> +xfs_inode_needs_inactive(
> +	struct xfs_inode	*ip)
> +{
> +	struct xfs_mount	*mp = ip->i_mount;
> +	struct xfs_ifork	*cow_ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
> +
> +	/*
> +	 * If the inode is already free, then there can be nothing
> +	 * to clean up here.
> +	 */
> +	if (VFS_I(ip)->i_mode == 0)
> +		return false;
> +
> +	/* If this is a read-only mount, don't do this (would generate I/O) */
> +	if (mp->m_flags & XFS_MOUNT_RDONLY)
> +		return false;
> +
> +	/* If the log isn't running, push inodes straight to reclaim. */
> +	if (XFS_FORCED_SHUTDOWN(mp) || (mp->m_flags & XFS_MOUNT_NORECOVERY))
> +		return false;
> +
> +	/* Metadata inodes require explicit resource cleanup. */
> +	if (xfs_is_metadata_inode(ip))
> +		return false;
> +
> +	/* Want to clean out the cow blocks if there are any. */
> +	if (cow_ifp && cow_ifp->if_bytes > 0)
> +		return true;
> +
> +	/* Unlinked files must be freed. */
> +	if (VFS_I(ip)->i_nlink == 0)
> +		return true;
> +
> +	/*
> +	 * This file isn't being freed, so check if there are post-eof blocks
> +	 * to free.  @force is true because we are evicting an inode from the
> +	 * cache.  Post-eof blocks must be freed, lest we end up with broken
> +	 * free space accounting.
> +	 *
> +	 * Note: don't bother with iolock here since lockdep complains about
> +	 * acquiring it in reclaim context. We have the only reference to the
> +	 * inode at this point anyways.
> +	 */
> +	return xfs_can_free_eofblocks(ip, true);
> +}
> +
>  /*
>   * xfs_inactive
>   *
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 4b6703dbffb8..e3137bbc7b14 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -493,6 +493,8 @@ extern struct kmem_zone	*xfs_inode_zone;
>  /* The default CoW extent size hint. */
>  #define XFS_DEFAULT_COWEXTSZ_HINT 32
>  
> +bool xfs_inode_needs_inactive(struct xfs_inode *ip);
> +
>  int xfs_iunlink_init(struct xfs_perag *pag);
>  void xfs_iunlink_destroy(struct xfs_perag *pag);
>  
>