Date:   Fri, 12 Feb 2021 09:15:41 -0800
From:   harshad shirwadkar <harshadshirwadkar@...il.com>
To:     Благодаренко Артём 
        <artem.blagodarenko@...il.com>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Alex Zhuravlev <bzzz@...mcloud.com>, sihara@....com,
        Andreas Dilger <adilger@...ger.ca>
Subject: Re: [PATCH v2 2/5] ext4: add mballoc stats proc file

Thanks Artem for pointing that out. The reason I added
s_bal_groups_considered inside ext4_mb_good_group() was that, in the
next patches in the series, the new allocator structures call
ext4_mb_good_group() before to check if the group looked up using cr0
lists or cr 1 tree is good or not. Having this counter incremented in
ext4_mb_good_group() helps us measure the overhead of the new
structures too. I'd like to keep that. But you're right, even without
those optimizations, ext4_mb_good_group() gets called twice. Which
means, with these optimizations it will get called 3 times. So,
perhaps we can increment s_bal_groups_considered in
ext4_mb_good_group_nolock() as you mentioned, and then we can also
increment it in the following patches just before calling
ext4_mb_good_group(). I'll note that for the next version, thanks!

- Harshad

On Fri, Feb 12, 2021 at 8:52 AM Благодаренко Артём
<artem.blagodarenko@...il.com> wrote:
>
> 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@...2 ~]# 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@...2 ~]# 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@...2 ~]#
>
> And location that suggested
> [root@...2 ~]# 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@...2 ~]# 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@...2 ~]#
>
> Second looks more rational.
>
> Best regards,
> Artem Blagodarenko.
>
> > On 9 Feb 2021, at 23:28, Harshad Shirwadkar <harshadshirwadkar@...il.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@...il.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
> >
>

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