Commit e30b5dca authored by Yan, Zheng's avatar Yan, Zheng Committed by Theodore Ts'o
Browse files

ext4: fix fio regression 



We (Linux Kernel Performance project) found a regression introduced
by commit:

  f7fec032 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: default avatarLKP project <lkp@linux.intel.com>
Signed-off-by: default avatarYan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: default avatarZheng Liu <wenqing.lz@taobao.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
parent 0d606e2c

fs/ext4/extents.c

+5 −4
Original line number Diff line number Diff line
@@ -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

fs/ext4/extents_status.c

+12 −5
Original line number Diff line number Diff line
@@ -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 *

fs/ext4/extents_status.h

+2 −1
Original line number Diff line number Diff line
@@ -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);

fs/ext4/file.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

include/trace/events/ext4.h

+2 −2
Original line number Diff line number Diff line
@@ -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),

CRA Git | Maintained and supported by SUSTech CRA and CCSE