xfs: use generic percpu counters for inode counter

XFS has hand-rolled per-cpu counters for the superblock since before
there was any generic implementation. There are some warts around
the  use of them for the inode counter as the hand rolled counter is
designed to be accurate at zero, but has no specific accurracy at
any other value. This design causes problems for the maximum inode
count threshold enforcement, as there is no trigger that balances
the counters as they get close tothe maximum threshold.

Instead of designing new triggers for balancing, just replace the
handrolled per-cpu counter with a generic counter.  This enables us
to update the counter through the normal superblock modification
funtions, but rather than do that we add a xfs_mod_icount() helper
function (from Christoph Hellwig) and keep the percpu counter
outside the superblock in the struct xfs_mount.

This means we still need to initialise the per-cpu counter
specifically when we read the superblock, and vice versa when we
log/write it, but it does mean that we don't need to change any
other code.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 35 insertions, 41 deletions

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 4fa80e63eea2..702ea6a7e648 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1099,6 +1099,21 @@ xfs_log_sbcount(xfs_mount_t *mp)
 	return xfs_sync_sb(mp, true);
 }
 
+int
+xfs_mod_icount(
+	struct xfs_mount	*mp,
+	int64_t			delta)
+{
+	/* deltas are +/-64, hence the large batch size of 128. */
+	__percpu_counter_add(&mp->m_icount, delta, 128);
+	if (percpu_counter_compare(&mp->m_icount, 0) < 0) {
+		ASSERT(0);
+		percpu_counter_add(&mp->m_icount, -delta);
+		return -EINVAL;
+	}
+	return 0;
+}
+
 /*
  * xfs_mod_incore_sb_unlocked() is a utility routine commonly used to apply
  * a delta to a specified field in the in-core superblock.  Simply
@@ -1127,14 +1142,8 @@ xfs_mod_incore_sb_unlocked(
 	 */
 	switch (field) {
 	case XFS_SBS_ICOUNT:
-		lcounter = (long long)mp->m_sb.sb_icount;
-		lcounter += delta;
-		if (lcounter < 0) {
-			ASSERT(0);
-			return -EINVAL;
-		}
-		mp->m_sb.sb_icount = lcounter;
-		return 0;
+		ASSERT(0);
+		return -ENOSPC;
 	case XFS_SBS_IFREE:
 		lcounter = (long long)mp->m_sb.sb_ifree;
 		lcounter += delta;
@@ -1288,8 +1297,9 @@ xfs_mod_incore_sb(
 	int			status;
 
 #ifdef HAVE_PERCPU_SB
-	ASSERT(field < XFS_SBS_ICOUNT || field > XFS_SBS_FDBLOCKS);
+	ASSERT(field < XFS_SBS_IFREE || field > XFS_SBS_FDBLOCKS);
 #endif
+
 	spin_lock(&mp->m_sb_lock);
 	status = xfs_mod_incore_sb_unlocked(mp, field, delta, rsvd);
 	spin_unlock(&mp->m_sb_lock);
@@ -1492,7 +1502,6 @@ xfs_icsb_cpu_notify(
 	case CPU_ONLINE:
 	case CPU_ONLINE_FROZEN:
 		xfs_icsb_lock(mp);
-		xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, 0);
 		xfs_icsb_balance_counter(mp, XFS_SBS_IFREE, 0);
 		xfs_icsb_balance_counter(mp, XFS_SBS_FDBLOCKS, 0);
 		xfs_icsb_unlock(mp);
@@ -1504,17 +1513,14 @@ xfs_icsb_cpu_notify(
 		 * re-enable the counters. */
 		xfs_icsb_lock(mp);
 		spin_lock(&mp->m_sb_lock);
-		xfs_icsb_disable_counter(mp, XFS_SBS_ICOUNT);
 		xfs_icsb_disable_counter(mp, XFS_SBS_IFREE);
 		xfs_icsb_disable_counter(mp, XFS_SBS_FDBLOCKS);
 
-		mp->m_sb.sb_icount += cntp->icsb_icount;
 		mp->m_sb.sb_ifree += cntp->icsb_ifree;
 		mp->m_sb.sb_fdblocks += cntp->icsb_fdblocks;
 
 		memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
 
-		xfs_icsb_balance_counter_locked(mp, XFS_SBS_ICOUNT, 0);
 		xfs_icsb_balance_counter_locked(mp, XFS_SBS_IFREE, 0);
 		xfs_icsb_balance_counter_locked(mp, XFS_SBS_FDBLOCKS, 0);
 		spin_unlock(&mp->m_sb_lock);
@@ -1531,11 +1537,18 @@ xfs_icsb_init_counters(
 	xfs_mount_t	*mp)
 {
 	xfs_icsb_cnts_t *cntp;
+	int		error;
 	int		i;
 
+	error = percpu_counter_init(&mp->m_icount, 0, GFP_KERNEL);
+	if (error)
+		return error;
+
 	mp->m_sb_cnts = alloc_percpu(xfs_icsb_cnts_t);
-	if (mp->m_sb_cnts == NULL)
+	if (!mp->m_sb_cnts) {
+		percpu_counter_destroy(&mp->m_icount);
 		return -ENOMEM;
+	}
 
 	for_each_online_cpu(i) {
 		cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
@@ -1563,13 +1576,14 @@ void
 xfs_icsb_reinit_counters(
 	xfs_mount_t	*mp)
 {
+	percpu_counter_set(&mp->m_icount, mp->m_sb.sb_icount);
+
 	xfs_icsb_lock(mp);
 	/*
 	 * start with all counters disabled so that the
 	 * initial balance kicks us off correctly
 	 */
 	mp->m_icsb_counters = -1;
-	xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, 0);
 	xfs_icsb_balance_counter(mp, XFS_SBS_IFREE, 0);
 	xfs_icsb_balance_counter(mp, XFS_SBS_FDBLOCKS, 0);
 	xfs_icsb_unlock(mp);
@@ -1583,6 +1597,9 @@ xfs_icsb_destroy_counters(
 		unregister_hotcpu_notifier(&mp->m_icsb_notifier);
 		free_percpu(mp->m_sb_cnts);
 	}
+
+	percpu_counter_destroy(&mp->m_icount);
+
 	mutex_destroy(&mp->m_icsb_mutex);
 }
 
@@ -1645,7 +1662,6 @@ xfs_icsb_count(
 
 	for_each_online_cpu(i) {
 		cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
-		cnt->icsb_icount += cntp->icsb_icount;
 		cnt->icsb_ifree += cntp->icsb_ifree;
 		cnt->icsb_fdblocks += cntp->icsb_fdblocks;
 	}
@@ -1659,7 +1675,7 @@ xfs_icsb_counter_disabled(
 	xfs_mount_t	*mp,
 	xfs_sb_field_t	field)
 {
-	ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));
+	ASSERT((field >= XFS_SBS_IFREE) && (field <= XFS_SBS_FDBLOCKS));
 	return test_bit(field, &mp->m_icsb_counters);
 }
 
@@ -1670,7 +1686,7 @@ xfs_icsb_disable_counter(
 {
 	xfs_icsb_cnts_t	cnt;
 
-	ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));
+	ASSERT((field >= XFS_SBS_IFREE) && (field <= XFS_SBS_FDBLOCKS));
 
 	/*
 	 * If we are already disabled, then there is nothing to do
@@ -1689,9 +1705,6 @@ xfs_icsb_disable_counter(
 
 		xfs_icsb_count(mp, &cnt, XFS_ICSB_LAZY_COUNT);
 		switch(field) {
-		case XFS_SBS_ICOUNT:
-			mp->m_sb.sb_icount = cnt.icsb_icount;
-			break;
 		case XFS_SBS_IFREE:
 			mp->m_sb.sb_ifree = cnt.icsb_ifree;
 			break;
@@ -1716,15 +1729,12 @@ xfs_icsb_enable_counter(
 	xfs_icsb_cnts_t	*cntp;
 	int		i;
 
-	ASSERT((field >= XFS_SBS_ICOUNT) && (field <= XFS_SBS_FDBLOCKS));
+	ASSERT((field >= XFS_SBS_IFREE) && (field <= XFS_SBS_FDBLOCKS));
 
 	xfs_icsb_lock_all_counters(mp);
 	for_each_online_cpu(i) {
 		cntp = per_cpu_ptr(mp->m_sb_cnts, i);
 		switch (field) {
-		case XFS_SBS_ICOUNT:
-			cntp->icsb_icount = count + resid;
-			break;
 		case XFS_SBS_IFREE:
 			cntp->icsb_ifree = count + resid;
 			break;
@@ -1750,8 +1760,6 @@ xfs_icsb_sync_counters_locked(
 
 	xfs_icsb_count(mp, &cnt, flags);
 
-	if (!xfs_icsb_counter_disabled(mp, XFS_SBS_ICOUNT))
-		mp->m_sb.sb_icount = cnt.icsb_icount;
 	if (!xfs_icsb_counter_disabled(mp, XFS_SBS_IFREE))
 		mp->m_sb.sb_ifree = cnt.icsb_ifree;
 	if (!xfs_icsb_counter_disabled(mp, XFS_SBS_FDBLOCKS))
@@ -1805,12 +1813,6 @@ xfs_icsb_balance_counter_locked(
 
 	/* update counters  - first CPU gets residual*/
 	switch (field) {
-	case XFS_SBS_ICOUNT:
-		count = mp->m_sb.sb_icount;
-		resid = do_div(count, weight);
-		if (count < max(min, XFS_ICSB_INO_CNTR_REENABLE))
-			return;
-		break;
 	case XFS_SBS_IFREE:
 		count = mp->m_sb.sb_ifree;
 		resid = do_div(count, weight);
@@ -1871,14 +1873,6 @@ again:
 	}
 
 	switch (field) {
-	case XFS_SBS_ICOUNT:
-		lcounter = icsbp->icsb_icount;
-		lcounter += delta;
-		if (unlikely(lcounter < 0))
-			goto balance_counter;
-		icsbp->icsb_icount = lcounter;
-		break;
-
 	case XFS_SBS_IFREE:
 		lcounter = icsbp->icsb_ifree;
 		lcounter += delta;