Hi Jan,
thanks for good suggestion, just one question we could not hold lock
with nojounal mode, how about something attached one?
please let me know if you have better taste for it, much appreciated!
Thanks,
Shilong
________________________________________
From: Jan Kara [jack@xxxxxxx]
Sent: Thursday, August 17, 2017 0:42
To: Wang Shilong
Cc: linux-ext4@xxxxxxxxxxxxxxx; tytso@xxxxxxx; Wang Shilong; adilger@xxxxxxxxx; Shuichi Ihara; Li Xi
Subject: Re: [PATCH v4] ext4: reduce lock contention in __ext4_new_inode
On Tue 08-08-17 13:05:17, Wang Shilong wrote:
> 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>
The results look great and the code looks correct however I dislike the
somewhat complex codeflow with your hold_lock variable. So how about
cleaning up the code as follows:
Create function like
unsigned long find_inode_bit(struct super_block *sb, ext4_group_t group,
struct buffer_head *bitmap, unsigned long start_ino)
{
unsigned long ino;
next:
ino = ext4_find_next_zero_bit(...);
if (ino >= EXT4_INODES_PER_GROUP(sb))
return 0;
if (group == 0 && (ino+1) < EXT4_FIRST_INO(sb)) {
...
return 0;
}
if ((EXT4_SB(sb)->s_journal == NULL) &&
recently_deleted(sb, group, ino)) {
start_ino = ino + 1;
if (start_ino < EXT4_INODES_PER_GROUP(sb))
goto next;
}
return ino;
}
Then you can use this function from __ext4_new_inode() when looking for
free ino and also in case test_and_set_bit() fails you could just do:
ext4_lock_group(sb, group);
ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
if (ret2) {
/* Someone already took the bit. Repeat the search with lock held.*/
ino = find_inode_bit(sb, group, inode_bitmap_bh, ino);
if (ino) {
ret2 = ext4_test_and_set_bit(ino, inode_bitmap_bh->b_data);
WARN_ON_ONCE(!ret2);
}
}
ext4_unlock_group(sb, group);
And that's it, no strange bool variables and conditional locking. And as a
bonus it also works for nojournal mode in the same way.
Honza
> ---
> 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
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
Attachment:
modfied.patch
Description: modfied.patch
