ext4: reduce reserved cluster count by number of allocated clusters

Ext4 does not always reduce the reserved cluster count by the number
of clusters allocated when mapping a delayed extent.  It sometimes
adds back one or more clusters after allocation if delalloc blocks
adjacent to the range allocated by ext4_ext_map_blocks() share the
clusters newly allocated for that range.  However, this overcounts
the number of clusters needed to satisfy future mapping requests
(holding one or more reservations for clusters that have already been
allocated) and premature ENOSPC and quota failures, etc., result.

Ext4 also does not reduce the reserved cluster count when allocating
clusters for non-delayed allocated writes that have previously been
reserved for delayed writes.  This also results in overcounts.

To make it possible to handle reserved cluster accounting for
fallocated regions in the same manner as used for other non-delayed
writes, do the reserved cluster accounting for them at the time of
allocation.  In the current code, this is only done later when a
delayed extent sharing the fallocated region is finally mapped.

Address comment correcting handling of unsigned long long constant
from Jan Kara's review of RFC version of this patch.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 175 insertions, 0 deletions

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index c5d456e12062..c92fbf444d08 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -150,6 +150,8 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 static int es_reclaim_extents(struct ext4_inode_info *ei, int *nr_to_scan);
 static int __es_shrink(struct ext4_sb_info *sbi, int nr_to_scan,
 		       struct ext4_inode_info *locked_ei);
+static void __revise_pending(struct inode *inode, ext4_lblk_t lblk,
+			     ext4_lblk_t len);
 
 int __init ext4_init_es(void)
 {
@@ -808,6 +810,7 @@ int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 	struct extent_status newes;
 	ext4_lblk_t end = lblk + len - 1;
 	int err = 0;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
 	es_debug("add [%u/%u) %llu %x to extent status tree of inode %lu\n",
 		 lblk, len, pblk, status, inode->i_ino);
@@ -844,6 +847,11 @@ retry:
 	if (err == -ENOMEM && !ext4_es_is_delayed(&newes))
 		err = 0;
 
+	if (sbi->s_cluster_ratio > 1 && test_opt(inode->i_sb, DELALLOC) &&
+	    (status & EXTENT_STATUS_WRITTEN ||
+	     status & EXTENT_STATUS_UNWRITTEN))
+		__revise_pending(inode, lblk, len);
+
 error:
 	write_unlock(&EXT4_I(inode)->i_es_lock);
 
@@ -1605,3 +1613,170 @@ error:
 
 	return err;
 }
+
+/*
+ * __es_delayed_clu - count number of clusters containing blocks that
+ *                    are delayed only
+ *
+ * @inode - file containing block range
+ * @start - logical block defining start of range
+ * @end - logical block defining end of range
+ *
+ * Returns the number of clusters containing only delayed (not delayed
+ * and unwritten) blocks in the range specified by @start and @end.  Any
+ * cluster or part of a cluster within the range and containing a delayed
+ * and not unwritten block within the range is counted as a whole cluster.
+ */
+static unsigned int __es_delayed_clu(struct inode *inode, ext4_lblk_t start,
+				     ext4_lblk_t end)
+{
+	struct ext4_es_tree *tree = &EXT4_I(inode)->i_es_tree;
+	struct extent_status *es;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	struct rb_node *node;
+	ext4_lblk_t first_lclu, last_lclu;
+	unsigned long long last_counted_lclu;
+	unsigned int n = 0;
+
+	/* guaranteed to be unequal to any ext4_lblk_t value */
+	last_counted_lclu = ~0ULL;
+
+	es = __es_tree_search(&tree->root, start);
+
+	while (es && (es->es_lblk <= end)) {
+		if (ext4_es_is_delonly(es)) {
+			if (es->es_lblk <= start)
+				first_lclu = EXT4_B2C(sbi, start);
+			else
+				first_lclu = EXT4_B2C(sbi, es->es_lblk);
+
+			if (ext4_es_end(es) >= end)
+				last_lclu = EXT4_B2C(sbi, end);
+			else
+				last_lclu = EXT4_B2C(sbi, ext4_es_end(es));
+
+			if (first_lclu == last_counted_lclu)
+				n += last_lclu - first_lclu;
+			else
+				n += last_lclu - first_lclu + 1;
+			last_counted_lclu = last_lclu;
+		}
+		node = rb_next(&es->rb_node);
+		if (!node)
+			break;
+		es = rb_entry(node, struct extent_status, rb_node);
+	}
+
+	return n;
+}
+
+/*
+ * ext4_es_delayed_clu - count number of clusters containing blocks that
+ *                       are both delayed and unwritten
+ *
+ * @inode - file containing block range
+ * @lblk - logical block defining start of range
+ * @len - number of blocks in range
+ *
+ * Locking for external use of __es_delayed_clu().
+ */
+unsigned int ext4_es_delayed_clu(struct inode *inode, ext4_lblk_t lblk,
+				 ext4_lblk_t len)
+{
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	ext4_lblk_t end;
+	unsigned int n;
+
+	if (len == 0)
+		return 0;
+
+	end = lblk + len - 1;
+	WARN_ON(end < lblk);
+
+	read_lock(&ei->i_es_lock);
+
+	n = __es_delayed_clu(inode, lblk, end);
+
+	read_unlock(&ei->i_es_lock);
+
+	return n;
+}
+
+/*
+ * __revise_pending - makes, cancels, or leaves unchanged pending cluster
+ *                    reservations for a specified block range depending
+ *                    upon the presence or absence of delayed blocks
+ *                    outside the range within clusters at the ends of the
+ *                    range
+ *
+ * @inode - file containing the range
+ * @lblk - logical block defining the start of range
+ * @len  - length of range in blocks
+ *
+ * Used after a newly allocated extent is added to the extents status tree.
+ * Requires that the extents in the range have either written or unwritten
+ * status.  Must be called while holding i_es_lock.
+ */
+static void __revise_pending(struct inode *inode, ext4_lblk_t lblk,
+			     ext4_lblk_t len)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+	ext4_lblk_t end = lblk + len - 1;
+	ext4_lblk_t first, last;
+	bool f_del = false, l_del = false;
+
+	if (len == 0)
+		return;
+
+	/*
+	 * Two cases - block range within single cluster and block range
+	 * spanning two or more clusters.  Note that a cluster belonging
+	 * to a range starting and/or ending on a cluster boundary is treated
+	 * as if it does not contain a delayed extent.  The new range may
+	 * have allocated space for previously delayed blocks out to the
+	 * cluster boundary, requiring that any pre-existing pending
+	 * reservation be canceled.  Because this code only looks at blocks
+	 * outside the range, it should revise pending reservations
+	 * correctly even if the extent represented by the range can't be
+	 * inserted in the extents status tree due to ENOSPC.
+	 */
+
+	if (EXT4_B2C(sbi, lblk) == EXT4_B2C(sbi, end)) {
+		first = EXT4_LBLK_CMASK(sbi, lblk);
+		if (first != lblk)
+			f_del = __es_scan_range(inode, &ext4_es_is_delonly,
+						first, lblk - 1);
+		if (f_del) {
+			__insert_pending(inode, first);
+		} else {
+			last = EXT4_LBLK_CMASK(sbi, end) +
+			       sbi->s_cluster_ratio - 1;
+			if (last != end)
+				l_del = __es_scan_range(inode,
+							&ext4_es_is_delonly,
+							end + 1, last);
+			if (l_del)
+				__insert_pending(inode, last);
+			else
+				__remove_pending(inode, last);
+		}
+	} else {
+		first = EXT4_LBLK_CMASK(sbi, lblk);
+		if (first != lblk)
+			f_del = __es_scan_range(inode, &ext4_es_is_delonly,
+						first, lblk - 1);
+		if (f_del)
+			__insert_pending(inode, first);
+		else
+			__remove_pending(inode, first);
+
+		last = EXT4_LBLK_CMASK(sbi, end) + sbi->s_cluster_ratio - 1;
+		if (last != end)
+			l_del = __es_scan_range(inode, &ext4_es_is_delonly,
+						end + 1, last);
+		if (l_del)
+			__insert_pending(inode, last);
+		else
+			__remove_pending(inode, last);
+	}
+}