ext4: optimize ext4_ext_convert_to_initialized()

This patch introduces a fast path in ext4_ext_convert_to_initialized()
for the case when the conversion can be performed by transferring
the newly initialized blocks from the uninitialized extent into
an adjacent initialized extent. Doing so removes the expensive
invocations of memmove() which occur during extent insertion and
the subsequent merge.

In practice this should be the common case for clients performing
append writes into files pre-allocated via
fallocate(FALLOC_FL_KEEP_SIZE). In such a workload performed via
direct IO and when using a suboptimal implementation of memmove()
(x86_64 prior to the 2.6.39 rewrite), this patch reduces kernel CPU
consumption by 32%.

Two new trace points are added to ext4_ext_convert_to_initialized()
to offer visibility into its operations. No exit trace point has
been added due to the multiplicity of return points. This can be
revisited once the upstream cleanup is backported.

Signed-off-by: Eric Gouriou <egouriou@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 82 insertions, 0 deletions

diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index c9a341e385a..748ff7cbe55 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -9,6 +9,7 @@
 
 struct ext4_allocation_context;
 struct ext4_allocation_request;
+struct ext4_extent;
 struct ext4_prealloc_space;
 struct ext4_inode_info;
 struct mpage_da_data;
@@ -1394,6 +1395,87 @@ DEFINE_EVENT(ext4__truncate, ext4_truncate_exit,
 	TP_ARGS(inode)
 );
 
+/* 'ux' is the uninitialized extent. */
+TRACE_EVENT(ext4_ext_convert_to_initialized_enter,
+	TP_PROTO(struct inode *inode, struct ext4_map_blocks *map,
+		 struct ext4_extent *ux),
+
+	TP_ARGS(inode, map, ux),
+
+	TP_STRUCT__entry(
+		__field(	ino_t,		ino	)
+		__field(	dev_t,		dev	)
+		__field(	ext4_lblk_t,	m_lblk	)
+		__field(	unsigned,	m_len	)
+		__field(	ext4_lblk_t,	u_lblk	)
+		__field(	unsigned,	u_len	)
+		__field(	ext4_fsblk_t,	u_pblk	)
+	),
+
+	TP_fast_assign(
+		__entry->ino		= inode->i_ino;
+		__entry->dev		= inode->i_sb->s_dev;
+		__entry->m_lblk		= map->m_lblk;
+		__entry->m_len		= map->m_len;
+		__entry->u_lblk		= le32_to_cpu(ux->ee_block);
+		__entry->u_len		= ext4_ext_get_actual_len(ux);
+		__entry->u_pblk		= ext4_ext_pblock(ux);
+	),
+
+	TP_printk("dev %d,%d ino %lu m_lblk %u m_len %u u_lblk %u u_len %u "
+		  "u_pblk %llu",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  (unsigned long) __entry->ino,
+		  __entry->m_lblk, __entry->m_len,
+		  __entry->u_lblk, __entry->u_len, __entry->u_pblk)
+);
+
+/*
+ * 'ux' is the uninitialized extent.
+ * 'ix' is the initialized extent to which blocks are transferred.
+ */
+TRACE_EVENT(ext4_ext_convert_to_initialized_fastpath,
+	TP_PROTO(struct inode *inode, struct ext4_map_blocks *map,
+		 struct ext4_extent *ux, struct ext4_extent *ix),
+
+	TP_ARGS(inode, map, ux, ix),
+
+	TP_STRUCT__entry(
+		__field(	ino_t,		ino	)
+		__field(	dev_t,		dev	)
+		__field(	ext4_lblk_t,	m_lblk	)
+		__field(	unsigned,	m_len	)
+		__field(	ext4_lblk_t,	u_lblk	)
+		__field(	unsigned,	u_len	)
+		__field(	ext4_fsblk_t,	u_pblk	)
+		__field(	ext4_lblk_t,	i_lblk	)
+		__field(	unsigned,	i_len	)
+		__field(	ext4_fsblk_t,	i_pblk	)
+	),
+
+	TP_fast_assign(
+		__entry->ino		= inode->i_ino;
+		__entry->dev		= inode->i_sb->s_dev;
+		__entry->m_lblk		= map->m_lblk;
+		__entry->m_len		= map->m_len;
+		__entry->u_lblk		= le32_to_cpu(ux->ee_block);
+		__entry->u_len		= ext4_ext_get_actual_len(ux);
+		__entry->u_pblk		= ext4_ext_pblock(ux);
+		__entry->i_lblk		= le32_to_cpu(ix->ee_block);
+		__entry->i_len		= ext4_ext_get_actual_len(ix);
+		__entry->i_pblk		= ext4_ext_pblock(ix);
+	),
+
+	TP_printk("dev %d,%d ino %lu m_lblk %u m_len %u "
+		  "u_lblk %u u_len %u u_pblk %llu "
+		  "i_lblk %u i_len %u i_pblk %llu ",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  (unsigned long) __entry->ino,
+		  __entry->m_lblk, __entry->m_len,
+		  __entry->u_lblk, __entry->u_len, __entry->u_pblk,
+		  __entry->i_lblk, __entry->i_len, __entry->i_pblk)
+);
+
 DECLARE_EVENT_CLASS(ext4__map_blocks_enter,
 	TP_PROTO(struct inode *inode, ext4_lblk_t lblk,
 		 unsigned int len, unsigned int flags),