From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>
We (Linux Kernel Performance project) found a regression introduced
by commit:
f7fec032aa ext4: track all extent status in extent status tree
The commit causes about 20% performance decrease in fio random write
test. Profiler shows that rb_next() uses a lot of CPU time. The call
stack is:
rb_next
ext4_es_find_delayed_extent
ext4_map_blocks
_ext4_get_block
ext4_get_block_write
__blockdev_direct_IO
ext4_direct_IO
generic_file_direct_write
__generic_file_aio_write
ext4_file_write
aio_rw_vect_retry
aio_run_iocb
do_io_submit
sys_io_submit
system_call_fastpath
io_submit
td_io_getevents
io_u_queued_complete
thread_main
main
__libc_start_main
The cause is that ext4_es_find_delayed_extent() doesn't have an
upper bound, it keeps searching until a delayed extent is found.
When there are a lots of non-delayed entries in the extent state
tree, ext4_es_find_delayed_extent() may uses a lot of CPU time.
Reported-by: LKP project <lkp@xxxxxxxxxxxxxxx>
Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
---
v2 <- v1:
* fix a off-by-one bug
fs/ext4/extents.c | 9 +++++----
fs/ext4/extents_status.c | 17 ++++++++++++-----
fs/ext4/extents_status.h | 3 ++-
fs/ext4/file.c | 4 ++--
include/trace/events/ext4.h | 4 ++--
5 files changed, 23 insertions(+), 14 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 107936d..bc0f191 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3642,7 +3642,7 @@ int ext4_find_delalloc_range(struct inode *inode,
{
struct extent_status es;
- ext4_es_find_delayed_extent(inode, lblk_start, &es);
+ ext4_es_find_delayed_extent_range(inode, lblk_start, lblk_end, &es);
if (es.es_len == 0)
return 0; /* there is no delay extent in this tree */
else if (es.es_lblk <= lblk_start &&
@@ -4608,9 +4608,10 @@ static int ext4_find_delayed_extent(struct inode *inode,
struct extent_status es;
ext4_lblk_t block, next_del;
- ext4_es_find_delayed_extent(inode, newes->es_lblk, &es);
-
if (newes->es_pblk == 0) {
+ ext4_es_find_delayed_extent_range(inode, newes->es_lblk,
+ newes->es_lblk + newes->es_len - 1, &es);
+
/*
* No extent in extent-tree contains block @newes->es_pblk,
* then the block may stay in 1)a hole or 2)delayed-extent.
@@ -4630,7 +4631,7 @@ static int ext4_find_delayed_extent(struct inode *inode,
}
block = newes->es_lblk + newes->es_len;
- ext4_es_find_delayed_extent(inode, block, &es);
+ ext4_es_find_delayed_extent_range(inode, block, EXT_MAX_BLOCKS, &es);
if (es.es_len == 0)
next_del = EXT_MAX_BLOCKS;
else
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index fe3337a..e6941e6 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -232,14 +232,16 @@ static struct extent_status *__es_tree_search(struct rb_root *root,
}
/*
- * ext4_es_find_delayed_extent: find the 1st delayed extent covering @es->lblk
- * if it exists, otherwise, the next extent after @es->lblk.
+ * ext4_es_find_delayed_extent_range: find the 1st delayed extent covering
+ * @es->lblk if it exists, otherwise, the next extent after @es->lblk.
*
* @inode: the inode which owns delayed extents
* @lblk: the offset where we start to search
+ * @end: the offset where we stop to search
* @es: delayed extent that we found
*/
-void ext4_es_find_delayed_extent(struct inode *inode, ext4_lblk_t lblk,
+void ext4_es_find_delayed_extent_range(struct inode *inode,
+ ext4_lblk_t lblk, ext4_lblk_t end,
struct extent_status *es)
{
struct ext4_es_tree *tree = NULL;
@@ -247,7 +249,8 @@ void ext4_es_find_delayed_extent(struct inode *inode, ext4_lblk_t lblk,
struct rb_node *node;
BUG_ON(es == NULL);
- trace_ext4_es_find_delayed_extent_enter(inode, lblk);
+ BUG_ON(end < lblk);
+ trace_ext4_es_find_delayed_extent_range_enter(inode, lblk);
read_lock(&EXT4_I(inode)->i_es_lock);
tree = &EXT4_I(inode)->i_es_tree;
@@ -270,6 +273,10 @@ out:
if (es1 && !ext4_es_is_delayed(es1)) {
while ((node = rb_next(&es1->rb_node)) != NULL) {
es1 = rb_entry(node, struct extent_status, rb_node);
+ if (es1->es_lblk > end) {
+ es1 = NULL;
+ break;
+ }
if (ext4_es_is_delayed(es1))
break;
}
@@ -285,7 +292,7 @@ out:
read_unlock(&EXT4_I(inode)->i_es_lock);
ext4_es_lru_add(inode);
- trace_ext4_es_find_delayed_extent_exit(inode, es);
+ trace_ext4_es_find_delayed_extent_range_exit(inode, es);
}
static struct extent_status *
diff --git a/fs/ext4/extents_status.h b/fs/ext4/extents_status.h
index d8e2d4d..f740eb03 100644
--- a/fs/ext4/extents_status.h
+++ b/fs/ext4/extents_status.h
@@ -62,7 +62,8 @@ extern int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
unsigned long long status);
extern int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
ext4_lblk_t len);
-extern void ext4_es_find_delayed_extent(struct inode *inode, ext4_lblk_t lblk,
+extern void ext4_es_find_delayed_extent_range(struct inode *inode,
+ ext4_lblk_t lblk, ext4_lblk_t end,
struct extent_status *es);
extern int ext4_es_lookup_extent(struct inode *inode, ext4_lblk_t lblk,
struct extent_status *es);
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 64848b5..1bc4523 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -464,7 +464,7 @@ static loff_t ext4_seek_data(struct file *file, loff_t offset, loff_t maxsize)
* If there is a delay extent at this offset,
* it will be as a data.
*/
- ext4_es_find_delayed_extent(inode, last, &es);
+ ext4_es_find_delayed_extent_range(inode, last, last, &es);
if (es.es_len != 0 && in_range(last, es.es_lblk, es.es_len)) {
if (last != start)
dataoff = last << blkbits;
@@ -547,7 +547,7 @@ static loff_t ext4_seek_hole(struct file *file, loff_t offset, loff_t maxsize)
* If there is a delay extent at this offset,
* we will skip this extent.
*/
- ext4_es_find_delayed_extent(inode, last, &es);
+ ext4_es_find_delayed_extent_range(inode, last, last, &es);
if (es.es_len != 0 && in_range(last, es.es_lblk, es.es_len)) {
last = es.es_lblk + es.es_len;
holeoff = last << blkbits;
diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index d0e6864..8ee15b9 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -2139,7 +2139,7 @@ TRACE_EVENT(ext4_es_remove_extent,
__entry->lblk, __entry->len)
);
-TRACE_EVENT(ext4_es_find_delayed_extent_enter,
+TRACE_EVENT(ext4_es_find_delayed_extent_range_enter,
TP_PROTO(struct inode *inode, ext4_lblk_t lblk),
TP_ARGS(inode, lblk),
@@ -2161,7 +2161,7 @@ TRACE_EVENT(ext4_es_find_delayed_extent_enter,
(unsigned long) __entry->ino, __entry->lblk)
);
-TRACE_EVENT(ext4_es_find_delayed_extent_exit,
+TRACE_EVENT(ext4_es_find_delayed_extent_range_exit,
TP_PROTO(struct inode *inode, struct extent_status *es),
TP_ARGS(inode, es),
--
1.7.12.rc2.18.g61b472e
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