Re: [PATCH v2 2/5] ext4: add mballoc stats proc file

["Благодаренко Артём" <artem.blagodarenko@gmail.com>]

Hello Harshad,

Thanks for this great work. I am still testing these patches. Right now I have noticed this flow -
s_bal_groups_considered is counted twice. It is placed to ext4_mb_good_group, that is called twice,
one time from  ext4_mb_good_group_nolock and again from  ext4_mb_good_group_nolock.
I’d rather put s_bal_groups_considered into the ext4_mb_good_group_nolock().

Here is simple execution (on non-fragmented partition) with old counter location

[root@CO82 ~]# dd if=/dev/zero of=/mnt/file4 bs=2M count=2 conv=fsync
2+0 records in
2+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0137407 s, 305 MB/s
[root@CO82 ~]# cat /proc/fs/ext4/sda2/mb_stats
mballoc:
    reqs: 2
    success: 1
    groups_scanned: 2
    groups_considered: 4
    extents_scanned: 2
        goal_hits: 0
        2^n_hits: 2
        breaks: 0
        lost: 0
    useless_c0_loops: 0
    useless_c1_loops: 0
    useless_c2_loops: 0
    useless_c3_loops: 0
    buddies_generated: 60/969
    buddies_time_used: 9178136
    preallocated: 5612
    discarded: 0
[root@CO82 ~]#

And location that suggested
[root@CO82 ~]# dd if=/dev/zero of=/mnt/file3 bs=2M count=2 conv=fsync
2+0 records in
2+0 records out
4194304 bytes (4.2 MB, 4.0 MiB) copied, 0.0155074 s, 270 MB/s
[root@CO82 ~]# cat /proc/fs/ext4/sda2/mb_stats
mballoc:
    reqs: 3
    success: 2
    groups_scanned: 2
    groups_considered: 2
    extents_scanned: 2
        goal_hits: 1
        2^n_hits: 2
        breaks: 0
        lost: 0
    useless_c0_loops: 0
    useless_c1_loops: 0
    useless_c2_loops: 0
    useless_c3_loops: 0
    buddies_generated: 60/969
    buddies_time_used: 2870959
    preallocated: 5626
    discarded: 0
[root@CO82 ~]#

Second looks more rational.

Best regards,
Artem Blagodarenko.

> On 9 Feb 2021, at 23:28, Harshad Shirwadkar <harshadshirwadkar@gmail.com> wrote:
> 
> Add new stats for measuring the performance of mballoc. This patch is
> forked from Artem Blagodarenko's work that can be found here:
> 
> https://github.com/lustre/lustre-release/blob/master/ldiskfs/kernel_patches/patches/rhel8/ext4-simple-blockalloc.patch
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
> ---
> fs/ext4/ext4.h    |  4 ++++
> fs/ext4/mballoc.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++-
> fs/ext4/mballoc.h |  1 +
> fs/ext4/sysfs.c   |  2 ++
> 4 files changed, 57 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 6dd127942208..317b43420ecf 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1549,6 +1549,8 @@ struct ext4_sb_info {
> 	atomic_t s_bal_success;	/* we found long enough chunks */
> 	atomic_t s_bal_allocated;	/* in blocks */
> 	atomic_t s_bal_ex_scanned;	/* total extents scanned */
> +	atomic_t s_bal_groups_considered;	/* number of groups considered */
> +	atomic_t s_bal_groups_scanned;	/* number of groups scanned */
> 	atomic_t s_bal_goals;	/* goal hits */
> 	atomic_t s_bal_breaks;	/* too long searches */
> 	atomic_t s_bal_2orders;	/* 2^order hits */
> @@ -1558,6 +1560,7 @@ struct ext4_sb_info {
> 	atomic_t s_mb_preallocated;
> 	atomic_t s_mb_discarded;
> 	atomic_t s_lock_busy;
> +	atomic64_t s_bal_cX_failed[4];		/* cX loop didn't find blocks */
> 
> 	/* locality groups */
> 	struct ext4_locality_group __percpu *s_locality_groups;
> @@ -2808,6 +2811,7 @@ int __init ext4_fc_init_dentry_cache(void);
> extern const struct seq_operations ext4_mb_seq_groups_ops;
> extern long ext4_mb_stats;
> extern long ext4_mb_max_to_scan;
> +extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);
> extern int ext4_mb_init(struct super_block *);
> extern int ext4_mb_release(struct super_block *);
> extern ext4_fsblk_t ext4_mb_new_blocks(handle_t *,
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 07b78a3cc421..fffd0770e930 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2083,6 +2083,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
> 
> 	BUG_ON(cr < 0 || cr >= 4);
> 
> +	ac->ac_groups_considered++;
> 	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
> 		return false;
> 
> @@ -2420,6 +2421,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> 			if (ac->ac_status != AC_STATUS_CONTINUE)
> 				break;
> 		}
> +		/* Processed all groups and haven't found blocks */
> +		if (sbi->s_mb_stats && i == ngroups)
> +			atomic64_inc(&sbi->s_bal_cX_failed[cr]);
> 	}
> 
> 	if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
> @@ -2548,6 +2552,48 @@ const struct seq_operations ext4_mb_seq_groups_ops = {
> 	.show   = ext4_mb_seq_groups_show,
> };
> 
> +int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
> +{
> +	struct super_block *sb = (struct super_block *)seq->private;
> +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> +
> +	seq_puts(seq, "mballoc:\n");
> +	if (!sbi->s_mb_stats) {
> +		seq_puts(seq, "\tmb stats collection turned off.\n");
> +		seq_puts(seq, "\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
> +		return 0;
> +	}
> +	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
> +	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
> +
> +	seq_printf(seq, "\tgroups_scanned: %u\n",  atomic_read(&sbi->s_bal_groups_scanned));
> +	seq_printf(seq, "\tgroups_considered: %u\n",  atomic_read(&sbi->s_bal_groups_considered));
> +	seq_printf(seq, "\textents_scanned: %u\n", atomic_read(&sbi->s_bal_ex_scanned));
> +	seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
> +	seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
> +	seq_printf(seq, "\t\tbreaks: %u\n", atomic_read(&sbi->s_bal_breaks));
> +	seq_printf(seq, "\t\tlost: %u\n", atomic_read(&sbi->s_mb_lost_chunks));
> +
> +	seq_printf(seq, "\tuseless_c0_loops: %llu\n",
> +		   (unsigned long long)atomic64_read(&sbi->s_bal_cX_failed[0]));
> +	seq_printf(seq, "\tuseless_c1_loops: %llu\n",
> +		   (unsigned long long)atomic64_read(&sbi->s_bal_cX_failed[1]));
> +	seq_printf(seq, "\tuseless_c2_loops: %llu\n",
> +		   (unsigned long long)atomic64_read(&sbi->s_bal_cX_failed[2]));
> +	seq_printf(seq, "\tuseless_c3_loops: %llu\n",
> +		   (unsigned long long)atomic64_read(&sbi->s_bal_cX_failed[3]));
> +	seq_printf(seq, "\tbuddies_generated: %u/%u\n",
> +		   atomic_read(&sbi->s_mb_buddies_generated),
> +		   ext4_get_groups_count(sb));
> +	seq_printf(seq, "\tbuddies_time_used: %llu\n",
> +		   atomic64_read(&sbi->s_mb_generation_time));
> +	seq_printf(seq, "\tpreallocated: %u\n",
> +		   atomic_read(&sbi->s_mb_preallocated));
> +	seq_printf(seq, "\tdiscarded: %u\n",
> +		   atomic_read(&sbi->s_mb_discarded));
> +	return 0;
> +}
> +
> static struct kmem_cache *get_groupinfo_cache(int blocksize_bits)
> {
> 	int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
> @@ -2968,9 +3014,10 @@ int ext4_mb_release(struct super_block *sb)
> 				atomic_read(&sbi->s_bal_reqs),
> 				atomic_read(&sbi->s_bal_success));
> 		ext4_msg(sb, KERN_INFO,
> -		      "mballoc: %u extents scanned, %u goal hits, "
> +		      "mballoc: %u extents scanned, %u groups scanned, %u goal hits, "
> 				"%u 2^N hits, %u breaks, %u lost",
> 				atomic_read(&sbi->s_bal_ex_scanned),
> +				atomic_read(&sbi->s_bal_groups_scanned),
> 				atomic_read(&sbi->s_bal_goals),
> 				atomic_read(&sbi->s_bal_2orders),
> 				atomic_read(&sbi->s_bal_breaks),
> @@ -3579,6 +3626,8 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
> 		if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
> 			atomic_inc(&sbi->s_bal_success);
> 		atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
> +		atomic_add(ac->ac_groups_scanned, &sbi->s_bal_groups_scanned);
> +		atomic_add(ac->ac_groups_considered, &sbi->s_bal_groups_considered);
> 		if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
> 				ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
> 			atomic_inc(&sbi->s_bal_goals);
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> index e75b4749aa1c..7597330dbdf8 100644
> --- a/fs/ext4/mballoc.h
> +++ b/fs/ext4/mballoc.h
> @@ -161,6 +161,7 @@ struct ext4_allocation_context {
> 	/* copy of the best found extent taken before preallocation efforts */
> 	struct ext4_free_extent ac_f_ex;
> 
> +	__u32 ac_groups_considered;
> 	__u16 ac_groups_scanned;
> 	__u16 ac_found;
> 	__u16 ac_tail;
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index 4e27fe6ed3ae..752d1c261e2a 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -527,6 +527,8 @@ int ext4_register_sysfs(struct super_block *sb)
> 					ext4_fc_info_show, sb);
> 		proc_create_seq_data("mb_groups", S_IRUGO, sbi->s_proc,
> 				&ext4_mb_seq_groups_ops, sb);
> +		proc_create_single_data("mb_stats", 0444, sbi->s_proc,
> +				ext4_seq_mb_stats_show, sb);
> 	}
> 	return 0;
> }
> -- 
> 2.30.0.478.g8a0d178c01-goog
>