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Message-Id: <20170806090501.45477-1-wshilong@ddn.com>
Date: Sun, 6 Aug 2017 17:05:01 +0800
From: Wang Shilong <wangshilong1991@...il.com>
To: linux-ext4@...r.kernel.org
Cc: tytso@....edu, wshilong@....com, adilger@...ger.ca, sihara@....com,
lixi@....com
Subject: [PATCH v3] ext4: reduce lock contention in __ext4_new_inode
From: Wang Shilong <wshilong@....com>
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@...0GHz, 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 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
ith patch:
File Creation File removal
609,982 281,461 ops/per second
611,971 276,029
612,027 280,225
611,159 282,631
611,001 271,177
Now creation performaces are improved about 8x with large journal size!!!!
The main problem here is we test inode bitmap and then lock and retest,
this might make us do repeat lock again and again which eat most of
cpu time.
the main reason we don't find free bit and set with lock held is we
need journal inode bitmap before test and set bit, however with
repeat logic, we could confirm journal stuff has been
properly setup after first try, another case is no journal
mode, however, that is not normal use, we could drop
to old way and schedule a bit for that.
Tested-by: Shuichi Ihara <sihara@....com>
Signed-off-by: Wang Shilong <wshilong@....com>
---
v2->v3: new approach
---
fs/ext4/ialloc.c | 46 +++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 41 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 507bfb3..de368f5 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)
@@ -917,21 +918,48 @@ 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 is
+ * journaled too, we can directly hold lock and
+ * set bit if found, this will avoid lock contention
+ * which make us retry again and again.
+ */
+ 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)) {
ext4_error(sb, "reserved inode found cleared - "
"inode=%lu", ino + 1);
+ if (hold_lock)
+ ext4_unlock_group(sb, group);
continue;
}
+
+ if (hold_lock) {
+ ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
+ ext4_unlock_group(sb, group);
+ ino++;
+ if (!ret2)
+ goto got;
+ BUG_ON(1);
+ }
+
if ((EXT4_SB(sb)->s_journal == NULL) &&
recently_deleted(sb, group, ino)) {
- ino++;
- goto next_inode;
+ if (++ino < EXT4_INODES_PER_GROUP(sb))
+ goto repeat_in_this_group;
+ else
+ goto next_group;
}
if (!handle) {
BUG_ON(nblocks <= 0);
@@ -950,15 +978,23 @@ 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);
ino++; /* the inode bitmap is zero-based */
if (!ret2)
goto got; /* we grabbed the inode! */
-next_inode:
- if (ino < EXT4_INODES_PER_GROUP(sb))
+ if (ino < EXT4_INODES_PER_GROUP(sb)) {
+ /* make no journal mode happy too */
+ if (!EXT4_SB(sb)->s_journal && ext4_fs_is_busy(sbi))
+ schedule_timeout_uninterruptible(
+ msecs_to_jiffies(1));
goto repeat_in_this_group;
+ }
next_group:
if (++group == ngroups)
group = 0;
--
2.9.3
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