[RFC PATCH 1/4] xfs: support deactivating AGs

From: Gao Xiang <hsiangkao@redhat.com>
To: linux-xfs@vger.kernel.org
Cc: Gao Xiang <hsiangkao@redhat.com>
Subject: [RFC PATCH 1/4] xfs: support deactivating AGs
Date: Thu, 15 Apr 2021 03:52:37 +0800	[thread overview]
Message-ID: <20210414195240.1802221-2-hsiangkao@redhat.com> (raw)
In-Reply-To: <20210414195240.1802221-1-hsiangkao@redhat.com>

To get rid of paralleled requests related to AGs which are pending
for shrinking, mark these perags as inactive rather than playing
with per-ag structures theirselves.

Since in that way, a per-ag lock can be used to stablize the inactive
status together with agi/agf buffer lock (which is much easier than
adding more complicated perag_{get, put} pairs..) Also, Such per-ags
can be released / reused when unmountfs / growfs.

On the read side, pag_inactive_rwsem can be unlocked immediately after
the agf or agi buffer lock is acquired. However, pag_inactive_rwsem
can only be unlocked after the agf/agi buffer locks are all acquired
with the inactive status on the write side.

XXX: maybe there are some missing cases.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/libxfs/xfs_ag.c     | 16 +++++++++++++---
 fs/xfs/libxfs/xfs_alloc.c  | 12 +++++++++++-
 fs/xfs/libxfs/xfs_ialloc.c | 26 +++++++++++++++++++++++++-
 fs/xfs/xfs_mount.c         |  2 ++
 fs/xfs/xfs_mount.h         |  6 ++++++
 5 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index c68a36688474..ba5702e5c9ad 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -676,16 +676,24 @@ xfs_ag_get_geometry(
 	if (agno >= mp->m_sb.sb_agcount)
 		return -EINVAL;
 
+	pag = xfs_perag_get(mp, agno);
+	down_read(&pag->pag_inactive_rwsem);
+
+	if (pag->pag_inactive) {
+		error = -EBUSY;
+		up_read(&pag->pag_inactive_rwsem);
+		goto out;
+	}
+
 	/* Lock the AG headers. */
 	error = xfs_ialloc_read_agi(mp, NULL, agno, &agi_bp);
+	up_read(&pag->pag_inactive_rwsem);
 	if (error)
-		return error;
+		goto out;
 	error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agf_bp);
 	if (error)
 		goto out_agi;
 
-	pag = agi_bp->b_pag;
-
 	/* Fill out form. */
 	memset(ageo, 0, sizeof(*ageo));
 	ageo->ag_number = agno;
@@ -707,5 +715,7 @@ xfs_ag_get_geometry(
 	xfs_buf_relse(agf_bp);
 out_agi:
 	xfs_buf_relse(agi_bp);
+out:
+	xfs_perag_put(pag);
 	return error;
 }
diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index aaa19101bb2a..01d4e4d4c1d6 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2537,12 +2537,17 @@ xfs_alloc_fix_freelist(
 	/* deferred ops (AGFL block frees) require permanent transactions */
 	ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
 
+	down_read(&pag->pag_inactive_rwsem);
+	if (pag->pag_inactive)
+		goto out_no_agbp;
+
 	if (!pag->pagf_init) {
 		error = xfs_alloc_read_agf(mp, tp, args->agno, flags, &agbp);
 		if (error) {
 			/* Couldn't lock the AGF so skip this AG. */
 			if (error == -EAGAIN)
 				error = 0;
+			up_read(&pag->pag_inactive_rwsem);
 			goto out_no_agbp;
 		}
 	}
@@ -2555,13 +2560,16 @@ xfs_alloc_fix_freelist(
 	if (pag->pagf_metadata && (args->datatype & XFS_ALLOC_USERDATA) &&
 	    (flags & XFS_ALLOC_FLAG_TRYLOCK)) {
 		ASSERT(!(flags & XFS_ALLOC_FLAG_FREEING));
+		up_read(&pag->pag_inactive_rwsem);
 		goto out_agbp_relse;
 	}
 
 	need = xfs_alloc_min_freelist(mp, pag);
 	if (!xfs_alloc_space_available(args, need, flags |
-			XFS_ALLOC_FLAG_CHECK))
+			XFS_ALLOC_FLAG_CHECK)) {
+		up_read(&pag->pag_inactive_rwsem);
 		goto out_agbp_relse;
+	}
 
 	/*
 	 * Get the a.g. freespace buffer.
@@ -2573,9 +2581,11 @@ xfs_alloc_fix_freelist(
 			/* Couldn't lock the AGF so skip this AG. */
 			if (error == -EAGAIN)
 				error = 0;
+			up_read(&pag->pag_inactive_rwsem);
 			goto out_no_agbp;
 		}
 	}
+	up_read(&pag->pag_inactive_rwsem);
 
 	/* reset a padding mismatched agfl before final free space check */
 	if (pag->pagf_agflreset)
diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index eefdb518fe64..4df218eeb088 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -969,11 +969,15 @@ xfs_ialloc_ag_select(
 	flags = XFS_ALLOC_FLAG_TRYLOCK;
 	for (;;) {
 		pag = xfs_perag_get(mp, agno);
+		down_read(&pag->pag_inactive_rwsem);
 		if (!pag->pagi_inodeok) {
 			xfs_ialloc_next_ag(mp);
 			goto nextag;
 		}
 
+		if (pag->pag_inactive)
+			goto nextag;
+
 		if (!pag->pagi_init) {
 			error = xfs_ialloc_pagi_init(mp, tp, agno);
 			if (error)
@@ -981,6 +985,7 @@ xfs_ialloc_ag_select(
 		}
 
 		if (pag->pagi_freecount) {
+			up_read(&pag->pag_inactive_rwsem);
 			xfs_perag_put(pag);
 			return agno;
 		}
@@ -1016,10 +1021,12 @@ xfs_ialloc_ag_select(
 
 		if (pag->pagf_freeblks >= needspace + ineed &&
 		    longest >= ineed) {
+			up_read(&pag->pag_inactive_rwsem);
 			xfs_perag_put(pag);
 			return agno;
 		}
 nextag:
+		up_read(&pag->pag_inactive_rwsem);
 		xfs_perag_put(pag);
 		/*
 		 * No point in iterating over the rest, if we're shutting
@@ -1776,10 +1783,13 @@ xfs_dialloc_select_ag(
 	agno = start_agno;
 	for (;;) {
 		pag = xfs_perag_get(mp, agno);
+		down_read(&pag->pag_inactive_rwsem);
 		if (!pag->pagi_inodeok) {
 			xfs_ialloc_next_ag(mp);
 			goto nextag;
 		}
+		if (pag->pag_inactive)
+			goto nextag;
 
 		if (!pag->pagi_init) {
 			error = xfs_ialloc_pagi_init(mp, *tpp, agno);
@@ -1802,6 +1812,7 @@ xfs_dialloc_select_ag(
 			break;
 
 		if (pag->pagi_freecount) {
+			up_read(&pag->pag_inactive_rwsem);
 			xfs_perag_put(pag);
 			goto found_ag;
 		}
@@ -1825,6 +1836,7 @@ xfs_dialloc_select_ag(
 			 * allocate one of the new inodes.
 			 */
 			ASSERT(pag->pagi_freecount > 0);
+			up_read(&pag->pag_inactive_rwsem);
 			xfs_perag_put(pag);
 
 			error = xfs_dialloc_roll(tpp, agbp);
@@ -1838,13 +1850,14 @@ xfs_dialloc_select_ag(
 nextag_relse_buffer:
 		xfs_trans_brelse(*tpp, agbp);
 nextag:
+		up_read(&pag->pag_inactive_rwsem);
 		xfs_perag_put(pag);
 		if (++agno == mp->m_sb.sb_agcount)
 			agno = 0;
 		if (agno == start_agno)
 			return noroom ? -ENOSPC : 0;
 	}
-
+	up_read(&pag->pag_inactive_rwsem);
 	xfs_perag_put(pag);
 	return error;
 found_ag:
@@ -2263,11 +2276,22 @@ xfs_imap_lookup(
 {
 	struct xfs_inobt_rec_incore rec;
 	struct xfs_btree_cur	*cur;
+	struct xfs_perag	*pag;
 	struct xfs_buf		*agbp;
 	int			error;
 	int			i;
 
+	pag = xfs_perag_get(mp, agno);
+	down_read(&pag->pag_inactive_rwsem);
+	if (pag->pag_inactive) {
+		up_read(&pag->pag_inactive_rwsem);
+		xfs_perag_put(pag);
+		return -EINVAL;
+	}
+
 	error = xfs_ialloc_read_agi(mp, tp, agno, &agbp);
+	up_read(&pag->pag_inactive_rwsem);
+	xfs_perag_put(pag);
 	if (error) {
 		xfs_alert(mp,
 			"%s: xfs_ialloc_read_agi() returned error %d, agno %d",
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 1c97b155a8ee..f86360514828 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -235,6 +235,8 @@ xfs_initialize_perag(
 		if (error)
 			goto out_hash_destroy;
 		spin_lock_init(&pag->pag_state_lock);
+
+		init_rwsem(&pag->pag_inactive_rwsem);
 	}
 
 	index = xfs_set_inode_alloc(mp, agcount);
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 81829d19596e..667dae0acaf9 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -309,6 +309,12 @@ typedef struct xfs_perag {
 	struct xfs_mount *pag_mount;	/* owner filesystem */
 	xfs_agnumber_t	pag_agno;	/* AG this structure belongs to */
 	atomic_t	pag_ref;	/* perag reference count */
+
+	struct rw_semaphore	pag_inactive_rwsem;
+	bool			pag_inactive;
+
+	/* zero the following fields when growfs pag_inactive == true pags */
+
 	char		pagf_init;	/* this agf's entry is initialized */
 	char		pagi_init;	/* this agi's entry is initialized */
 	char		pagf_metadata;	/* the agf is preferred to be metadata */
-- 
2.27.0

