[PATCH v6 6/7] xfs: support shrinking unused space in the last AG

From: Gao Xiang <hsiangkao@redhat.com>
To: linux-xfs@vger.kernel.org
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
	Brian Foster <bfoster@redhat.com>,
	Eric Sandeen <sandeen@sandeen.net>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@infradead.org>,
	Gao Xiang <hsiangkao@redhat.com>
Subject: [PATCH v6 6/7] xfs: support shrinking unused space in the last AG
Date: Tue, 26 Jan 2021 20:56:20 +0800	[thread overview]
Message-ID: <20210126125621.3846735-7-hsiangkao@redhat.com> (raw)
In-Reply-To: <20210126125621.3846735-1-hsiangkao@redhat.com>

As the first step of shrinking, this attempts to enable shrinking
unused space in the last allocation group by fixing up freespace
btree, agi, agf and adjusting super block and use a helper
xfs_ag_shrink_space() to fixup the last AG.

This can be all done in one transaction for now, so I think no
additional protection is needed.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/xfs_fsops.c | 64 ++++++++++++++++++++++++++++++----------------
 fs/xfs/xfs_trans.c |  1 -
 2 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 6c4ab5e31054..4bcea22f7b3f 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -38,7 +38,7 @@ xfs_resizefs_init_new_ags(
 	struct aghdr_init_data	*id,
 	xfs_agnumber_t		oagcount,
 	xfs_agnumber_t		nagcount,
-	xfs_rfsblock_t		*delta)
+	int64_t			*delta)
 {
 	xfs_rfsblock_t		nb = mp->m_sb.sb_dblocks + *delta;
 	int			error;
@@ -76,33 +76,41 @@ xfs_growfs_data_private(
 	xfs_agnumber_t		nagcount;
 	xfs_agnumber_t		nagimax = 0;
 	xfs_rfsblock_t		nb, nb_div, nb_mod;
-	xfs_rfsblock_t		delta;
+	int64_t			delta;
 	xfs_agnumber_t		oagcount;
 	struct xfs_trans	*tp;
+	bool			extend;
 	struct aghdr_init_data	id = {};
 
 	nb = in->newblocks;
-	if (nb < mp->m_sb.sb_dblocks)
-		return -EINVAL;
-	if ((error = xfs_sb_validate_fsb_count(&mp->m_sb, nb)))
+	if (nb == mp->m_sb.sb_dblocks)
+		return 0;
+
+	error = xfs_sb_validate_fsb_count(&mp->m_sb, nb);
+	if (error)
 		return error;
-	error = xfs_buf_read_uncached(mp->m_ddev_targp,
+
+	if (nb > mp->m_sb.sb_dblocks) {
+		error = xfs_buf_read_uncached(mp->m_ddev_targp,
 				XFS_FSB_TO_BB(mp, nb) - XFS_FSS_TO_BB(mp, 1),
 				XFS_FSS_TO_BB(mp, 1), 0, &bp, NULL);
-	if (error)
-		return error;
-	xfs_buf_relse(bp);
+		if (error)
+			return error;
+		xfs_buf_relse(bp);
+	}
 
 	nb_div = nb;
 	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
 	nagcount = nb_div + (nb_mod != 0);
 	if (nb_mod && nb_mod < XFS_MIN_AG_BLOCKS) {
 		nagcount--;
-		nb = (xfs_rfsblock_t)nagcount * mp->m_sb.sb_agblocks;
-		if (nb < mp->m_sb.sb_dblocks)
+		if (nagcount < 2)
 			return -EINVAL;
+		nb = (xfs_rfsblock_t)nagcount * mp->m_sb.sb_agblocks;
 	}
+
 	delta = nb - mp->m_sb.sb_dblocks;
+	extend = (delta > 0);
 	oagcount = mp->m_sb.sb_agcount;
 
 	/* allocate the new per-ag structures */
@@ -110,22 +118,34 @@ xfs_growfs_data_private(
 		error = xfs_initialize_perag(mp, nagcount, &nagimax);
 		if (error)
 			return error;
+	} else if (nagcount < oagcount) {
+		/* TODO: shrinking the entire AGs hasn't yet completed */
+		return -EINVAL;
 	}
 
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata,
-			XFS_GROWFS_SPACE_RES(mp), 0, XFS_TRANS_RESERVE, &tp);
+			(extend ? XFS_GROWFS_SPACE_RES(mp) : -delta), 0,
+			XFS_TRANS_RESERVE, &tp);
 	if (error)
 		return error;
 
-	error = xfs_resizefs_init_new_ags(mp, &id, oagcount, nagcount, &delta);
-	if (error)
-		goto out_trans_cancel;
-
+	if (extend) {
+		error = xfs_resizefs_init_new_ags(mp, &id, oagcount,
+						  nagcount, &delta);
+		if (error)
+			goto out_trans_cancel;
+	}
 	xfs_trans_agblocks_delta(tp, id.nfree);
 
-	/* If there are new blocks in the old last AG, extend it. */
+	/* If there are some blocks in the last AG, resize it. */
 	if (delta) {
-		error = xfs_ag_extend_space(mp, tp, &id, delta);
+		if (extend) {
+			error = xfs_ag_extend_space(mp, tp, &id, delta);
+		} else {
+			id.agno = nagcount - 1;
+			error = xfs_ag_shrink_space(mp, &tp, &id, -delta);
+		}
+
 		if (error)
 			goto out_trans_cancel;
 	}
@@ -137,15 +157,15 @@ xfs_growfs_data_private(
 	 */
 	if (nagcount > oagcount)
 		xfs_trans_mod_sb(tp, XFS_TRANS_SB_AGCOUNT, nagcount - oagcount);
-	if (nb > mp->m_sb.sb_dblocks)
+	if (nb != mp->m_sb.sb_dblocks)
 		xfs_trans_mod_sb(tp, XFS_TRANS_SB_DBLOCKS,
 				 nb - mp->m_sb.sb_dblocks);
 	if (id.nfree)
 		xfs_trans_mod_sb(tp, XFS_TRANS_SB_FDBLOCKS, id.nfree);
 
 	/*
-	 * update in-core counters now to reflect the real numbers
-	 * (especially sb_fdblocks)
+	 * update in-core counters now to reflect the real numbers (especially
+	 * sb_fdblocks). And xfs_validate_sb_write() can pass for shrinkfs.
 	 */
 	if (xfs_sb_version_haslazysbcount(&mp->m_sb))
 		xfs_log_sb(tp);
@@ -165,7 +185,7 @@ xfs_growfs_data_private(
 	 * If we expanded the last AG, free the per-AG reservation
 	 * so we can reinitialize it with the new size.
 	 */
-	if (delta) {
+	if (extend && delta) {
 		struct xfs_perag	*pag;
 
 		pag = xfs_perag_get(mp, id.agno);
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index e72730f85af1..fd2cbf414b80 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -419,7 +419,6 @@ xfs_trans_mod_sb(
 		tp->t_res_frextents_delta += delta;
 		break;
 	case XFS_TRANS_SB_DBLOCKS:
-		ASSERT(delta > 0);
 		tp->t_dblocks_delta += delta;
 		break;
 	case XFS_TRANS_SB_AGCOUNT:
-- 
2.27.0

