Re: [PATCH 6/6] xfs: refactor per-AG inode tagging functions

From: "Darrick J. Wong" <djwong@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-xfs@vger.kernel.org
Subject: Re: [PATCH 6/6] xfs: refactor per-AG inode tagging functions
Date: Fri, 26 Mar 2021 09:34:10 -0700	[thread overview]
Message-ID: <20210326163410.GX4090233@magnolia> (raw)
In-Reply-To: <20210326064809.GG3421955@infradead.org>

On Fri, Mar 26, 2021 at 06:48:09AM +0000, Christoph Hellwig wrote:
> On Thu, Mar 25, 2021 at 05:21:46PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > In preparation for adding another incore inode tree tag, refactor the
> > code that sets and clears tags from the per-AG inode tree and the tree
> > of per-AG structures, and remove the open-coded versions used by the
> > blockgc code.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  fs/xfs/xfs_icache.c |  127 ++++++++++++++++++++++++---------------------------
> >  fs/xfs/xfs_icache.h |    2 -
> >  fs/xfs/xfs_super.c  |    2 -
> >  fs/xfs/xfs_trace.h  |    6 +-
> >  4 files changed, 65 insertions(+), 72 deletions(-)
> > 
> > 
> > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
> > index 2b25fe679b0e..4c124bc98f39 100644
> > --- a/fs/xfs/xfs_icache.c
> > +++ b/fs/xfs/xfs_icache.c
> > @@ -29,6 +29,7 @@
> >  /* Forward declarations to reduce indirect calls */
> >  static int xfs_blockgc_scan_inode(struct xfs_inode *ip,
> >  		struct xfs_eofblocks *eofb);
> > +static inline void xfs_blockgc_queue(struct xfs_perag *pag);
> >  static bool xfs_reclaim_inode_grab(struct xfs_inode *ip);
> >  static void xfs_reclaim_inode(struct xfs_inode *ip, struct xfs_perag *pag);
> >  
> > @@ -163,46 +164,78 @@ xfs_reclaim_work_queue(
> >  	rcu_read_unlock();
> >  }
> >  
> > +/* Set a tag on both the AG incore inode tree and the AG radix tree. */
> >  static void
> > +xfs_perag_set_ici_tag(
> > +	struct xfs_perag	*pag,
> > +	xfs_agino_t		agino,
> > +	unsigned int		tag)
> 
> Looking at the callers - I think the logic to lookup the pag and set the
> inode flag should also go in here.

I deliberately didn't do that here because of what happens in the
deferred inactivation patch.  After calling xfs_inactive, we have to
transition the inode from INACTIVATING to RECLAIMABLE (along with the
radix tree tags) without anybody being able to see intermediate state:

	/*
	 * Move the inode from the inactivation phase to the reclamation phase
	 * by clearing both inactivation inode state flags and marking the
	 * inode reclaimable.  Schedule background reclaim to run later.
	 */
	spin_lock(&pag->pag_ici_lock);
	spin_lock(&ip->i_flags_lock);

	ip->i_flags &= ~(XFS_NEED_INACTIVE | XFS_INACTIVATING);
	ip->i_flags |= XFS_IRECLAIMABLE;

	xfs_perag_clear_ici_tag(pag, agino, XFS_ICI_INODEGC_TAG);
	xfs_perag_set_ici_tag(pag, agino, XFS_ICI_RECLAIM_TAG);

	spin_unlock(&ip->i_flags_lock);
	spin_unlock(&pag->pag_ici_lock);

Which is why the xfs_perag_*_ici_tag callers are left in charge of
looking up the pag and taking locks as needed.

> Currently only xfs_inode_destroy
> nests i_Flags log inside the pag_ici_lock, but I don't see how that
> would harm the xfs_blockgc_set_iflag case.

The other wart is that IEOFBLOCKS and ICOWBLOCKS share the same radix
tree tag, which complicates the clearing logic, and I thought it best
to let the callers deal with that.

> I suspect the unlocked
> check in xfs_blockgc_set_iflag would harm in the reclaim case either.

"wouldn't"?

> 
> >  void
> > +xfs_inode_destroy(
> 
> I find this new name a little confusing.  What about
> xfs_inode_mark_reclaimable?

Fixed.

> But overall this new scheme looks nice to me.

Thanks!

--D