[PATCH v2 v2 0/2] add blocks_allocated to mb_stats and clear mb_stats

[PATCH v2 v2 0/2] add blocks_allocated to mb_stats and clear mb_stats

[Baolin Liu]

This series improves ext4 mballoc statistics in two small ways.

The first patch adds blocks_allocated to /proc/fs/ext4/<dev>/mb_stats,
so that the proc output covers the same mballoc summary counters
printed at unmount time.

The second patch makes /proc/fs/ext4/<dev>/mb_stats writable
and allows writing 0 to clear the current runtime mballoc statistics.

Changes since v1: 
 - Split blocks_allocated reporting and statistics clearing into two patches
 - Drop the separate mb_stats_clear sysfs node
 - Make /proc/fs/ext4/<dev>/mb_stats writable instead

Baolin Liu (2):
  ext4: add blocks_allocated to mb_stats output
  ext4: allow clearing mballoc stats through mb_stats

 fs/ext4/ext4.h    |  1 +
 fs/ext4/mballoc.c | 31 +++++++++++++++++++++++++++++++
 fs/ext4/sysfs.c   | 40 ++++++++++++++++++++++++++++++++++++++--
 3 files changed, 70 insertions(+), 2 deletions(-)

-- 
2.51.0

[PATCH v2 v2 1/2] ext4: add blocks_allocated to mb_stats output

[Baolin Liu]

From: Baolin Liu <liubaolin@kylinos.cn>

Add blocks_allocated to /proc/fs/ext4/<dev>/mb_stats so that the
reported statistics match the mballoc summary printed at unmount time.

Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
 fs/ext4/mballoc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 20e9fdaf4301..1e13ef62cb9d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3211,6 +3211,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 			"\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
 		return 0;
 	}
+	seq_printf(seq, "\tblocks_allocated: %u\n",
+		   atomic_read(&sbi->s_bal_allocated));
 	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
 	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
 
-- 
2.51.0

[PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Baolin Liu]

From: Baolin Liu <liubaolin@kylinos.cn>

Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
mballoc statistics when 0 is written.

Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
 fs/ext4/ext4.h    |  1 +
 fs/ext4/mballoc.c | 29 +++++++++++++++++++++++++++++
 fs/ext4/sysfs.c   | 40 ++++++++++++++++++++++++++++++++++++++--
 3 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 293f698b7042..3223e73612ae 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2994,6 +2994,7 @@ int ext4_fc_record_regions(struct super_block *sb, int ino,
 extern const struct seq_operations ext4_mb_seq_groups_ops;
 extern const struct seq_operations ext4_mb_seq_structs_summary_ops;
 extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);
+extern void ext4_mb_stats_clear(struct ext4_sb_info *sbi);
 extern int ext4_mb_init(struct super_block *);
 extern void 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 1e13ef62cb9d..79ddfa935813 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4723,6 +4723,35 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
 		trace_ext4_mballoc_prealloc(ac);
 }
 
+void ext4_mb_stats_clear(struct ext4_sb_info *sbi)
+{
+	int i;
+
+	atomic_set(&sbi->s_bal_reqs, 0);
+	atomic_set(&sbi->s_bal_success, 0);
+	atomic_set(&sbi->s_bal_allocated, 0);
+	atomic_set(&sbi->s_bal_groups_scanned, 0);
+
+	for (i = 0; i < EXT4_MB_NUM_CRS; i++) {
+		atomic64_set(&sbi->s_bal_cX_hits[i], 0);
+		atomic64_set(&sbi->s_bal_cX_groups_considered[i], 0);
+		atomic_set(&sbi->s_bal_cX_ex_scanned[i], 0);
+		atomic64_set(&sbi->s_bal_cX_failed[i], 0);
+	}
+
+	atomic_set(&sbi->s_bal_ex_scanned, 0);
+	atomic_set(&sbi->s_bal_goals, 0);
+	atomic_set(&sbi->s_bal_stream_goals, 0);
+	atomic_set(&sbi->s_bal_len_goals, 0);
+	atomic_set(&sbi->s_bal_2orders, 0);
+	atomic_set(&sbi->s_bal_breaks, 0);
+	atomic_set(&sbi->s_mb_lost_chunks, 0);
+	atomic_set(&sbi->s_mb_buddies_generated, 0);
+	atomic64_set(&sbi->s_mb_generation_time, 0);
+	atomic_set(&sbi->s_mb_preallocated, 0);
+	atomic_set(&sbi->s_mb_discarded, 0);
+}
+
 /*
  * Called on failure; free up any blocks from the inode PA for this
  * context.  We don't need this for MB_GROUP_PA because we only change
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index b87d7bdab06a..e90885d470ab 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -52,6 +52,42 @@ typedef enum {
 static const char proc_dirname[] = "fs/ext4";
 static struct proc_dir_entry *ext4_proc_root;
 
+static int ext4_mb_stats_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ext4_seq_mb_stats_show, pde_data(inode));
+}
+
+static ssize_t ext4_mb_stats_write(struct file *file, const char __user *buf,
+					   size_t count, loff_t *ppos)
+{
+	struct super_block *sb = pde_data(file_inode(file));
+	char kbuf[2];
+
+	if (count == 0 || count > sizeof(kbuf))
+		return -EINVAL;
+
+	if (copy_from_user(kbuf, buf, count))
+		return -EFAULT;
+
+	if (count == 2) {
+		if (kbuf[0] != '0' || kbuf[1] != '\n')
+			return -EINVAL;
+	} else if (kbuf[0] != '0') {
+		return -EINVAL;
+	}
+
+	ext4_mb_stats_clear(EXT4_SB(sb));
+	return count;
+}
+
+static const struct proc_ops ext4_mb_stats_proc_ops = {
+	.proc_open	= ext4_mb_stats_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= ext4_mb_stats_write,
+};
+
 struct ext4_attr {
 	struct attribute attr;
 	short attr_id;
@@ -630,8 +666,8 @@ 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);
+		proc_create_data("mb_stats", 0644, sbi->s_proc,
+				 &ext4_mb_stats_proc_ops, sb);
 		proc_create_seq_data("mb_structs_summary", 0444, sbi->s_proc,
 				&ext4_mb_seq_structs_summary_ops, sb);
 	}
-- 
2.51.0

Re: [PATCH v2 v2 1/2] ext4: add blocks_allocated to mb_stats output

[Andreas Dilger]

On Apr 19, 2026, at 00:34, Baolin Liu <liubaolin12138@163.com> wrote:
> 
> From: Baolin Liu <liubaolin@kylinos.cn>
> 
> Add blocks_allocated to /proc/fs/ext4/<dev>/mb_stats so that the
> reported statistics match the mballoc summary printed at unmount time.
> 
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>

Reviewed-by: Andreas Dilger <adilger@dilger.ca <mailto:adilger@dilger.ca>>

> ---
> fs/ext4/mballoc.c | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 20e9fdaf4301..1e13ef62cb9d 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3211,6 +3211,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq,
>  			"\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
>  		return 0;
>  	}
> +	seq_printf(seq, "\tblocks_allocated: %u\n",
> +		   atomic_read(&sbi->s_bal_allocated));
>  	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
>  	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
> 
> -- 
> 2.51.0
> 


Cheers, Andreas

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Andreas Dilger]

On Apr 19, 2026, at 00:34, Baolin Liu <liubaolin12138@163.com> wrote:
> 
> From: Baolin Liu <liubaolin@kylinos.cn>
> 
> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
> mballoc statistics when 0 is written.
> 
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>

Reviewed-by: Andreas Dilger <adilger@dilger.ca <mailto:adilger@dilger.ca>>

> ---
> fs/ext4/ext4.h    |  1 +
> fs/ext4/mballoc.c | 29 +++++++++++++++++++++++++++++
> fs/ext4/sysfs.c   | 40 ++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 68 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 293f698b7042..3223e73612ae 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2994,6 +2994,7 @@ int ext4_fc_record_regions(struct super_block *sb, int ino,
> extern const struct seq_operations ext4_mb_seq_groups_ops;
> extern const struct seq_operations ext4_mb_seq_structs_summary_ops;
> extern int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset);
> +extern void ext4_mb_stats_clear(struct ext4_sb_info *sbi);
> extern int ext4_mb_init(struct super_block *);
> extern void 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 1e13ef62cb9d..79ddfa935813 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4723,6 +4723,35 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
> trace_ext4_mballoc_prealloc(ac);
> }
> 
> +void ext4_mb_stats_clear(struct ext4_sb_info *sbi)
> +{
> +	int i;
> +
> +	atomic_set(&sbi->s_bal_reqs, 0);
> +	atomic_set(&sbi->s_bal_success, 0);
> +	atomic_set(&sbi->s_bal_allocated, 0);
> +	atomic_set(&sbi->s_bal_groups_scanned, 0);
> +
> +	for (i = 0; i < EXT4_MB_NUM_CRS; i++) {
> +		atomic64_set(&sbi->s_bal_cX_hits[i], 0);
> +		atomic64_set(&sbi->s_bal_cX_groups_considered[i], 0);
> +		atomic_set(&sbi->s_bal_cX_ex_scanned[i], 0);
> +		atomic64_set(&sbi->s_bal_cX_failed[i], 0);
> +	}
> +
> +	atomic_set(&sbi->s_bal_ex_scanned, 0);
> +	atomic_set(&sbi->s_bal_goals, 0);
> +	atomic_set(&sbi->s_bal_stream_goals, 0);
> +	atomic_set(&sbi->s_bal_len_goals, 0);
> +	atomic_set(&sbi->s_bal_2orders, 0);
> +	atomic_set(&sbi->s_bal_breaks, 0);
> +	atomic_set(&sbi->s_mb_lost_chunks, 0);
> +	atomic_set(&sbi->s_mb_buddies_generated, 0);
> +	atomic64_set(&sbi->s_mb_generation_time, 0);
> +	atomic_set(&sbi->s_mb_preallocated, 0);
> +	atomic_set(&sbi->s_mb_discarded, 0);
> +}
> +
> /*
>  * Called on failure; free up any blocks from the inode PA for this
>  * context.  We don't need this for MB_GROUP_PA because we only change
> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
> index b87d7bdab06a..e90885d470ab 100644
> --- a/fs/ext4/sysfs.c
> +++ b/fs/ext4/sysfs.c
> @@ -52,6 +52,42 @@ typedef enum {
> static const char proc_dirname[] = "fs/ext4";
> static struct proc_dir_entry *ext4_proc_root;
> 
> +static int ext4_mb_stats_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, ext4_seq_mb_stats_show, pde_data(inode));
> +}
> +
> +static ssize_t ext4_mb_stats_write(struct file *file, const char __user *buf,
> +				   size_t count, loff_t *ppos)
> +{
> +	struct super_block *sb = pde_data(file_inode(file));
> +	char kbuf[2];
> +
> +	if (count == 0 || count > sizeof(kbuf))
> +		return -EINVAL;
> +
> +	if (copy_from_user(kbuf, buf, count))
> +		return -EFAULT;
> +
> +	if (count == 2) {
> +		if (kbuf[0] != '0' || kbuf[1] != '\n')
> +			return -EINVAL;
> +	} else if (kbuf[0] != '0') {
> +		return -EINVAL;
> +	}
> +
> +	ext4_mb_stats_clear(EXT4_SB(sb));
> +	return count;
> +}
> +
> +static const struct proc_ops ext4_mb_stats_proc_ops = {
> +	.proc_open	= ext4_mb_stats_open,
> +	.proc_read	= seq_read,
> +	.proc_lseek	= seq_lseek,
> +	.proc_release	= single_release,
> +	.proc_write	= ext4_mb_stats_write,
> +};
> +
>  struct ext4_attr {
>  	struct attribute attr;
>  	short attr_id;
> @@ -630,8 +666,8 @@ 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);
> +		proc_create_data("mb_stats", 0644, sbi->s_proc,
> +				 &ext4_mb_stats_proc_ops, sb);
>  		proc_create_seq_data("mb_structs_summary", 0444, sbi->s_proc,
>  				&ext4_mb_seq_structs_summary_ops, sb);
> }
> -- 
> 2.51.0
> 


Cheers, Andreas

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Ojaswin Mujoo]

On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
> From: Baolin Liu <liubaolin@kylinos.cn>
> 
> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
> mballoc statistics when 0 is written.
> 
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
> ---
Hi Baolin, thanks for the changes.

Seems like userspace doesn't have any way to know that writing 0 will
clear the that. Well, I guess if you are looking at this file you are
anyways debugging kernel code so that should be fine

Feel free to add:

Ojaswin Mujoo <ojaswin@linux.ibm.com>

Regards,
ojaswin


>  fs/ext4/ext4.h    |  1 +
>  fs/ext4/mballoc.c | 29 +++++++++++++++++++++++++++++
>  fs/ext4/sysfs.c   | 40 ++++++++++++++++++++++++++++++++++++++--
>  3 files changed, 68 insertions(+), 2 deletions(-)
> 

Re: [PATCH v2 v2 1/2] ext4: add blocks_allocated to mb_stats output

[Ojaswin Mujoo]

On Sun, Apr 19, 2026 at 02:34:35PM +0800, Baolin Liu wrote:
> From: Baolin Liu <liubaolin@kylinos.cn>
> 
> Add blocks_allocated to /proc/fs/ext4/<dev>/mb_stats so that the
> reported statistics match the mballoc summary printed at unmount time.
> 
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
> ---

Looks good,

Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>

Regards,
ojaswin

>  fs/ext4/mballoc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 20e9fdaf4301..1e13ef62cb9d 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3211,6 +3211,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
>  			"\tTo enable, please write \"1\" to sysfs file mb_stats.\n");
>  		return 0;
>  	}
> +	seq_printf(seq, "\tblocks_allocated: %u\n",
> +		   atomic_read(&sbi->s_bal_allocated));
>  	seq_printf(seq, "\treqs: %u\n", atomic_read(&sbi->s_bal_reqs));
>  	seq_printf(seq, "\tsuccess: %u\n", atomic_read(&sbi->s_bal_success));
>  
> -- 
> 2.51.0
> 

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Andreas Dilger]

On Apr 20, 2026, at 03:12, Ojaswin Mujoo <ojaswin@linux.ibm.com> wrote:
> 
> On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
>> From: Baolin Liu <liubaolin@kylinos.cn>
>> 
>> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
>> mballoc statistics when 0 is written.
>> 
>> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
>> ---
> Hi Baolin, thanks for the changes.
> 
> Seems like userspace doesn't have any way to know that writing 0 will
> clear the that. Well, I guess if you are looking at this file you are
> anyways debugging kernel code so that should be fine

That could be documented in Documentation/filesystems/ext4/allocators.rst,
or better would be to add a new file that covers mballoc in more detail.

Cheers, Andreas

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Ritesh Harjani]

Andreas Dilger <adilger@dilger.ca> writes:

> On Apr 20, 2026, at 03:12, Ojaswin Mujoo <ojaswin@linux.ibm.com> wrote:
>> 
>> On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
>>> From: Baolin Liu <liubaolin@kylinos.cn>
>>> 
>>> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
>>> mballoc statistics when 0 is written.
>>> 
>>> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
>>> ---
>> Hi Baolin, thanks for the changes.
>> 
>> Seems like userspace doesn't have any way to know that writing 0 will
>> clear the that. Well, I guess if you are looking at this file you are
>> anyways debugging kernel code so that should be fine
>
> That could be documented in Documentation/filesystems/ext4/allocators.rst,
> or better would be to add a new file that covers mballoc in more detail.
>

I started looking for ext4's control knobs for sys-admins in kernel
Documentation where we should ideally document this, and I see those
are declared here..

Documentation/admin-guide/ext4.rst
Documentation/ABI/testing/sysfs-fs-ext4.rst

Looking at this and the relevant code, I see all /proc/ entries in ext4
are all readable and sysfs entries for ext4 are mostly the control knobs
which are declared in above admin guide.

But now this patch adds a control knob to /proc/fs/ext4/<dev>/mb_stats,
to clear the stats :).

I guess we could have simply documented a new control knob value (e.g.
"2") for clearing the stats via /sys/fs/ext4/<dev>/mb_stats itself or
maybe even having mb_stats_clear file in sysfs wasn't bad either... But
either ways, clearing the stats via the same procfs mb_stats file is not
totally bad and I don't have a strong preference.


For documenting this, we can add mb_stats entry under /proc section in
Documentation/admin-guide/ext4.rst and document this change. Something
like - 

  mb_stats
        reports runtime statistics from multiblock allocator (mballoc),
        including allocation request counts, groups scanned,
        per-criteria scan hits (cr_p2_aligned, cr_goal_fast,
        cr_best_avail, cr_goal_slow, cr_any_free), groups / extents
        scanned, goal hits, buddy bitmap generations, and preallocation
        usage etc.
        Writing 0 to this procfs file resets all counters to zero.


-ritesh

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[liubaolin]

Dear all,
    I noticed the discussion about where to document the ext4 proc 
parameter mb_stats.
    I ran:
      git grep -n "/proc/fs/ext4" Documentation/
    and found that ext4 proc parameters are currently documented in both
    Documentation/admin-guide/ext4.rst and 
Documentation/filesystems/proc.rst.

    To be consistent with the existing documentation, I am thinking 
about documenting mb_stats in both places.
    If there are no objections, I will send a v3 shortly.
    Compared with v2,the v3 patch will add the mb_stats documentation to 
both ext4.rst and proc.rst.

    Regards,
    Baolin



在 2026/4/21 11:40, Ritesh Harjani (IBM) 写道:
> Andreas Dilger <adilger@dilger.ca> writes:
> 
>> On Apr 20, 2026, at 03:12, Ojaswin Mujoo <ojaswin@linux.ibm.com> wrote:
>>>
>>> On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
>>>> From: Baolin Liu <liubaolin@kylinos.cn>
>>>>
>>>> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
>>>> mballoc statistics when 0 is written.
>>>>
>>>> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
>>>> ---
>>> Hi Baolin, thanks for the changes.
>>>
>>> Seems like userspace doesn't have any way to know that writing 0 will
>>> clear the that. Well, I guess if you are looking at this file you are
>>> anyways debugging kernel code so that should be fine
>>
>> That could be documented in Documentation/filesystems/ext4/allocators.rst,
>> or better would be to add a new file that covers mballoc in more detail.
>>
> 
> I started looking for ext4's control knobs for sys-admins in kernel
> Documentation where we should ideally document this, and I see those
> are declared here..
> 
> Documentation/admin-guide/ext4.rst
> Documentation/ABI/testing/sysfs-fs-ext4.rst
> 
> Looking at this and the relevant code, I see all /proc/ entries in ext4
> are all readable and sysfs entries for ext4 are mostly the control knobs
> which are declared in above admin guide.
> 
> But now this patch adds a control knob to /proc/fs/ext4/<dev>/mb_stats,
> to clear the stats :).
> 
> I guess we could have simply documented a new control knob value (e.g.
> "2") for clearing the stats via /sys/fs/ext4/<dev>/mb_stats itself or
> maybe even having mb_stats_clear file in sysfs wasn't bad either... But
> either ways, clearing the stats via the same procfs mb_stats file is not
> totally bad and I don't have a strong preference.
> 
> 
> For documenting this, we can add mb_stats entry under /proc section in
> Documentation/admin-guide/ext4.rst and document this change. Something
> like -
> 
>    mb_stats
>          reports runtime statistics from multiblock allocator (mballoc),
>          including allocation request counts, groups scanned,
>          per-criteria scan hits (cr_p2_aligned, cr_goal_fast,
>          cr_best_avail, cr_goal_slow, cr_any_free), groups / extents
>          scanned, goal hits, buddy bitmap generations, and preallocation
>          usage etc.
>          Writing 0 to this procfs file resets all counters to zero.
> 
> 
> -ritesh

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[Ojaswin Mujoo]

On Tue, Apr 21, 2026 at 01:22:31PM +0800, liubaolin wrote:
> Dear all,
>    I noticed the discussion about where to document the ext4 proc parameter
> mb_stats.
>    I ran:
>      git grep -n "/proc/fs/ext4" Documentation/
>    and found that ext4 proc parameters are currently documented in both
>    Documentation/admin-guide/ext4.rst and
> Documentation/filesystems/proc.rst.
> 
>    To be consistent with the existing documentation, I am thinking about
> documenting mb_stats in both places.
>    If there are no objections, I will send a v3 shortly.
>    Compared with v2,the v3 patch will add the mb_stats documentation to both
> ext4.rst and proc.rst.

Yes this makes sense to me. Feel free to retain the Reviewed-by since this is
just a documentation change.

Thanks,
Ojaswin

> 
>    Regards,
>    Baolin
> 
> 
> 
> 在 2026/4/21 11:40, Ritesh Harjani (IBM) 写道:
> > Andreas Dilger <adilger@dilger.ca> writes:
> > 
> > > On Apr 20, 2026, at 03:12, Ojaswin Mujoo <ojaswin@linux.ibm.com> wrote:
> > > > 
> > > > On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
> > > > > From: Baolin Liu <liubaolin@kylinos.cn>
> > > > > 
> > > > > Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
> > > > > mballoc statistics when 0 is written.
> > > > > 
> > > > > Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
> > > > > ---
> > > > Hi Baolin, thanks for the changes.
> > > > 
> > > > Seems like userspace doesn't have any way to know that writing 0 will
> > > > clear the that. Well, I guess if you are looking at this file you are
> > > > anyways debugging kernel code so that should be fine
> > > 
> > > That could be documented in Documentation/filesystems/ext4/allocators.rst,
> > > or better would be to add a new file that covers mballoc in more detail.
> > > 
> > 
> > I started looking for ext4's control knobs for sys-admins in kernel
> > Documentation where we should ideally document this, and I see those
> > are declared here..
> > 
> > Documentation/admin-guide/ext4.rst
> > Documentation/ABI/testing/sysfs-fs-ext4.rst
> > 
> > Looking at this and the relevant code, I see all /proc/ entries in ext4
> > are all readable and sysfs entries for ext4 are mostly the control knobs
> > which are declared in above admin guide.
> > 
> > But now this patch adds a control knob to /proc/fs/ext4/<dev>/mb_stats,
> > to clear the stats :).
> > 
> > I guess we could have simply documented a new control knob value (e.g.
> > "2") for clearing the stats via /sys/fs/ext4/<dev>/mb_stats itself or
> > maybe even having mb_stats_clear file in sysfs wasn't bad either... But
> > either ways, clearing the stats via the same procfs mb_stats file is not
> > totally bad and I don't have a strong preference.
> > 
> > 
> > For documenting this, we can add mb_stats entry under /proc section in
> > Documentation/admin-guide/ext4.rst and document this change. Something
> > like -
> > 
> >    mb_stats
> >          reports runtime statistics from multiblock allocator (mballoc),
> >          including allocation request counts, groups scanned,
> >          per-criteria scan hits (cr_p2_aligned, cr_goal_fast,
> >          cr_best_avail, cr_goal_slow, cr_any_free), groups / extents
> >          scanned, goal hits, buddy bitmap generations, and preallocation
> >          usage etc.
> >          Writing 0 to this procfs file resets all counters to zero.
> > 
> > 
> > -ritesh
> 

Re: [PATCH v2 v2 2/2] ext4: allow clearing mballoc stats through mb_stats

[liubaolin]

在 2026/4/21 14:12, Ojaswin Mujoo 写道:
> On Tue, Apr 21, 2026 at 01:22:31PM +0800, liubaolin wrote:
>> Dear all,
>>     I noticed the discussion about where to document the ext4 proc parameter
>> mb_stats.
>>     I ran:
>>       git grep -n "/proc/fs/ext4" Documentation/
>>     and found that ext4 proc parameters are currently documented in both
>>     Documentation/admin-guide/ext4.rst and
>> Documentation/filesystems/proc.rst.
>>
>>     To be consistent with the existing documentation, I am thinking about
>> documenting mb_stats in both places.
>>     If there are no objections, I will send a v3 shortly.
>>     Compared with v2,the v3 patch will add the mb_stats documentation to both
>> ext4.rst and proc.rst.
> 
> Yes this makes sense to me. Feel free to retain the Reviewed-by since this is
> just a documentation change.

> OK, I will add all the reviewers who helped review my patch with Reviewed-by tags in the v3 version.


> 
> Thanks,
> Ojaswin
> 
>>
>>     Regards,
>>     Baolin
>>
>>
>>
>> 在 2026/4/21 11:40, Ritesh Harjani (IBM) 写道:
>>> Andreas Dilger <adilger@dilger.ca> writes:
>>>
>>>> On Apr 20, 2026, at 03:12, Ojaswin Mujoo <ojaswin@linux.ibm.com> wrote:
>>>>>
>>>>> On Sun, Apr 19, 2026 at 02:34:36PM +0800, Baolin Liu wrote:
>>>>>> From: Baolin Liu <liubaolin@kylinos.cn>
>>>>>>
>>>>>> Make /proc/fs/ext4/<dev>/mb_stats writable and clear the runtime
>>>>>> mballoc statistics when 0 is written.
>>>>>>
>>>>>> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
>>>>>> ---
>>>>> Hi Baolin, thanks for the changes.
>>>>>
>>>>> Seems like userspace doesn't have any way to know that writing 0 will
>>>>> clear the that. Well, I guess if you are looking at this file you are
>>>>> anyways debugging kernel code so that should be fine
>>>>
>>>> That could be documented in Documentation/filesystems/ext4/allocators.rst,
>>>> or better would be to add a new file that covers mballoc in more detail.
>>>>
>>>
>>> I started looking for ext4's control knobs for sys-admins in kernel
>>> Documentation where we should ideally document this, and I see those
>>> are declared here..
>>>
>>> Documentation/admin-guide/ext4.rst
>>> Documentation/ABI/testing/sysfs-fs-ext4.rst
>>>
>>> Looking at this and the relevant code, I see all /proc/ entries in ext4
>>> are all readable and sysfs entries for ext4 are mostly the control knobs
>>> which are declared in above admin guide.
>>>
>>> But now this patch adds a control knob to /proc/fs/ext4/<dev>/mb_stats,
>>> to clear the stats :).
>>>
>>> I guess we could have simply documented a new control knob value (e.g.
>>> "2") for clearing the stats via /sys/fs/ext4/<dev>/mb_stats itself or
>>> maybe even having mb_stats_clear file in sysfs wasn't bad either... But
>>> either ways, clearing the stats via the same procfs mb_stats file is not
>>> totally bad and I don't have a strong preference.
>>>
>>>
>>> For documenting this, we can add mb_stats entry under /proc section in
>>> Documentation/admin-guide/ext4.rst and document this change. Something
>>> like -
>>>
>>>     mb_stats
>>>           reports runtime statistics from multiblock allocator (mballoc),
>>>           including allocation request counts, groups scanned,
>>>           per-criteria scan hits (cr_p2_aligned, cr_goal_fast,
>>>           cr_best_avail, cr_goal_slow, cr_any_free), groups / extents
>>>           scanned, goal hits, buddy bitmap generations, and preallocation
>>>           usage etc.
>>>           Writing 0 to this procfs file resets all counters to zero.
>>>
>>>
>>> -ritesh
>>