From: Wang Shilong <wshilong@xxxxxxx>
While running number of creating file threads concurrently,
we found heavy lock contention on group spinlock:
FUNC TOTAL_TIME(us) COUNT AVG(us)
ext4_create 1707443399 1440000 1185.72
_raw_spin_lock 1317641501 180899929 7.28
jbd2__journal_start 287821030 1453950 197.96
jbd2_journal_get_write_access 33441470 73077185 0.46
ext4_add_nondir 29435963 1440000 20.44
ext4_add_entry 26015166 1440049 18.07
ext4_dx_add_entry 25729337 1432814 17.96
ext4_mark_inode_dirty 12302433 5774407 2.13
most of cpu time blames to _raw_spin_lock, here is some testing
numbers with/without patch.
Test environment:
Server : SuperMicro Sever (2 x E5-2690 v3@2.60GHz, 128GB 2133MHz
DDR4 Memory, 8GbFC)
Storage : 2 x RAID1 (DDN SFA7700X, 4 x Toshiba PX02SMU020 200GB
Read Intensive SSD)
format command:
mkfs.ext4 -J size=4096
test command:
mpirun -np 48 mdtest -n 30000 -d /ext4/mdtest.out -F -C \
-r -i 1 -v -p 10 -u #first run to load inode
mpirun -np 48 mdtest -n 30000 -d /ext4/mdtest.out -F -C \
-r -i 5 -v -p 10 -u
Kernel version: 4.13.0-rc3
Test 1,440,000 files with 48 directories by 48 processes:
Without patch:
File Creation File removal
79,033 289,569 ops/per second
81,463 285,359
79,875 288,475
79,917 284,624
79,420 290,91
with patch:
File Creation File removal
691,528 296,574 ops/per second
691,946 297,106
692,030 296,238
691,005 299,249
692,871 300,664
Creation performance is improved more than 8X with large
journal size. The main problem here is we test bitmap
and do some check and journal operations which could be
slept, then we test and set with lock hold, this could
be racy, and make 'inode' steal by other process.
However, after first try, we could confirm handle has
been started and inode bitmap journaled too, then
we could find and set bit with lock hold directly, this
will mostly gurateee success with second try.
This patch dosen't change logic if it comes to
no journal mode, luckily this is not normal
use cases i believe.
Tested-by: Shuichi Ihara <sihara@xxxxxxx>
Signed-off-by: Wang Shilong <wshilong@xxxxxxx>
---
v3->v4: codes cleanup and avoid sleep.
---
fs/ext4/ialloc.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 507bfb3..23380f39 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -761,6 +761,7 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
ext4_group_t flex_group;
struct ext4_group_info *grp;
int encrypt = 0;
+ bool hold_lock;
/* Cannot create files in a deleted directory */
if (!dir || !dir->i_nlink)
@@ -917,17 +918,40 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
continue;
}
+ hold_lock = false;
repeat_in_this_group:
+ /* if @hold_lock is ture, that means, journal
+ * is properly setup and inode bitmap buffer has
+ * been journaled already, we can directly hold
+ * lock and set bit if found, this will mostly
+ * gurantee forward progress for each thread.
+ */
+ if (hold_lock)
+ ext4_lock_group(sb, group);
+
ino = ext4_find_next_zero_bit((unsigned long *)
inode_bitmap_bh->b_data,
EXT4_INODES_PER_GROUP(sb), ino);
- if (ino >= EXT4_INODES_PER_GROUP(sb))
+ if (ino >= EXT4_INODES_PER_GROUP(sb)) {
+ if (hold_lock)
+ ext4_unlock_group(sb, group);
goto next_group;
+ }
if (group == 0 && (ino+1) < EXT4_FIRST_INO(sb)) {
+ if (hold_lock)
+ ext4_unlock_group(sb, group);
ext4_error(sb, "reserved inode found cleared - "
"inode=%lu", ino + 1);
continue;
}
+
+ if (hold_lock) {
+ ext4_set_bit(ino, inode_bitmap_bh->b_data);
+ ext4_unlock_group(sb, group);
+ ino++;
+ goto got;
+ }
+
if ((EXT4_SB(sb)->s_journal == NULL) &&
recently_deleted(sb, group, ino)) {
ino++;
@@ -950,6 +974,10 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
ext4_std_error(sb, err);
goto out;
}
+
+ if (EXT4_SB(sb)->s_journal)
+ hold_lock = true;
+
ext4_lock_group(sb, group);
ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
ext4_unlock_group(sb, group);
--
2.9.3
