[PATCH v3 v3 0/2] add blocks_allocated to mb_stats and clear mb_stats

[PATCH v3 v3 0/2] add blocks_allocated to mb_stats and clear mb_stats

[Baolin Liu]

The series contains two patches:
 - add blocks_allocated to /proc/fs/ext4/<dev>/mb_stats
 - allow writing 0 to /proc/fs/ext4/<dev>/mb_stats to clear the current
   mballoc statistics

Changes since v2: 
 - Add mb_stats documentation to patch 2
 - Add Reviewed-by tags

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

 Documentation/admin-guide/ext4.rst |  5 ++++
 Documentation/filesystems/proc.rst |  3 +++
 fs/ext4/ext4.h                     |  1 +
 fs/ext4/mballoc.c                  | 31 +++++++++++++++++++++++
 fs/ext4/sysfs.c                    | 40 ++++++++++++++++++++++++++++--
 5 files changed, 78 insertions(+), 2 deletions(-)

-- 
2.51.0

[PATCH v3 v3 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.

Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
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 v3 v3 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.
Update the related documentation accordingly.

Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
 Documentation/admin-guide/ext4.rst |  5 ++++
 Documentation/filesystems/proc.rst |  3 +++
 fs/ext4/ext4.h                     |  1 +
 fs/ext4/mballoc.c                  | 29 ++++++++++++++++++++++
 fs/ext4/sysfs.c                    | 40 ++++++++++++++++++++++++++++--
 5 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/ext4.rst b/Documentation/admin-guide/ext4.rst
index ac0c709ea9e7..fb3887cd5e44 100644
--- a/Documentation/admin-guide/ext4.rst
+++ b/Documentation/admin-guide/ext4.rst
@@ -436,6 +436,11 @@ Files in /proc/fs/ext4/<devname>
   mb_groups
         details of multiblock allocator buddy cache of free blocks
 
+  mb_stats
+        reports runtime statistics from the multiblock allocator
+        (mballoc). Writing 0 to this file clears the current
+        statistics.
+
 /sys entries
 ============
 
diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index b0c0d1b45b99..7ce02573a3d9 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -1634,6 +1634,9 @@ directory are shown in Table 1-12, below.
  ==============  ==========================================================
  File            Content
  mb_groups       details of multiblock allocator buddy cache of free blocks
+ mb_stats        reports runtime statistics from the multiblock allocator
+                 (mballoc). Writing 0 to this file clears the current
+                 statistics.
  ==============  ==========================================================
 
 1.9 /proc/consoles
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 v3 v3 0/2] add blocks_allocated to mb_stats and clear mb_stats

[liubaolin]

在 2026/4/22 9:50, Baolin Liu 写道:
> The series contains two patches:
>   - add blocks_allocated to /proc/fs/ext4/<dev>/mb_stats
>   - allow writing 0 to /proc/fs/ext4/<dev>/mb_stats to clear the current
>     mballoc statistics
> 
> Changes since v2:
>   - Add mb_stats documentation to patch 2
>   - Add Reviewed-by tags
> 
> Baolin Liu (2):
>    ext4: add blocks_allocated to mb_stats output
>    ext4: allow clearing mballoc stats through mb_stats
> 
>   Documentation/admin-guide/ext4.rst |  5 ++++
>   Documentation/filesystems/proc.rst |  3 +++
>   fs/ext4/ext4.h                     |  1 +
>   fs/ext4/mballoc.c                  | 31 +++++++++++++++++++++++
>   fs/ext4/sysfs.c                    | 40 ++++++++++++++++++++++++++++--
>   5 files changed, 78 insertions(+), 2 deletions(-)
> 
Dear All,
    This commit adds the description of the ext4 proc parameter mb_stats 
to the corresponding documentation.
    I noticed that the documentation also lacks descriptions for the 
es_shrinker_info, fc_info, mb_structs_summary, and options parameters.
    However, these parameters are irrelevant to the work done in this 
series of patches.
    I will commit a separate patch later to explain the other parameters.
    This time, I only explain mb_stats.

    Thanks,
    Baolin

Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats

[Theodore Tso]

On Wed, Apr 22, 2026 at 09:50:25AM +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.

At the moment to enable mb_stats the system administrator needs to
write "1" to /sys/fs/ext4/<dev>/mb_stats, and writing "0" to the sysfs
file will pauce the statistics colleciton (but not clear the
statistics).  Adding a way to clear the statistics by writing to the
procfs file might be confusing to users.

So.... as a suggestion, if you're adding to the ability to write to
/proc/fs/.../mb_stats, what if we make things work by

   * Write 1 to /proc/fs/.../mb_stats to  enable statistics collection
   * Write 0 to /proc/fs/.../mb_stats to  disable statistics collection
   * Write -1 to /proc/fs/.../mb_stats to clear statistics counters

And then deprecate the /sys/fs/.../mb_stats variable (but we probably
won't be able to remove it for at least a year or two).

	       	       	  	    	- Ted

Re: [PATCH v3 v3 1/2] ext4: add blocks_allocated to mb_stats output

[Baokun Li]

On 2026/4/22 09:50, 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.
>
> Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
> Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>

Looks good, feel free to add:

Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>

> ---
>  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));
>  

Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats

[Baokun Li]

On 2026/4/24 00:19, Theodore Tso wrote:
> On Wed, Apr 22, 2026 at 09:50:25AM +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.
> At the moment to enable mb_stats the system administrator needs to
> write "1" to /sys/fs/ext4/<dev>/mb_stats, and writing "0" to the sysfs
> file will pauce the statistics colleciton (but not clear the
> statistics).  Adding a way to clear the statistics by writing to the
> procfs file might be confusing to users.
>
> So.... as a suggestion, if you're adding to the ability to write to
> /proc/fs/.../mb_stats, what if we make things work by
>
>    * Write 1 to /proc/fs/.../mb_stats to  enable statistics collection
>    * Write 0 to /proc/fs/.../mb_stats to  disable statistics collection
>    * Write -1 to /proc/fs/.../mb_stats to clear statistics counters
>
> And then deprecate the /sys/fs/.../mb_stats variable (but we probably
> won't be able to remove it for at least a year or two).

I like this idea. Consolidating everything into /proc/fs/.../mb_stats
and using -1 to reset the counters is much cleaner than the current
split approach.


Cheers,
Baokun

Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats

[liubaolin]

在 2026/4/24 0:19, Theodore Tso 写道:
> On Wed, Apr 22, 2026 at 09:50:25AM +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.
> 
> At the moment to enable mb_stats the system administrator needs to
> write "1" to /sys/fs/ext4/<dev>/mb_stats, and writing "0" to the sysfs
> file will pauce the statistics colleciton (but not clear the
> statistics).  Adding a way to clear the statistics by writing to the
> procfs file might be confusing to users.
> 
> So.... as a suggestion, if you're adding to the ability to write to
> /proc/fs/.../mb_stats, what if we make things work by
> 
>     * Write 1 to /proc/fs/.../mb_stats to  enable statistics collection
>     * Write 0 to /proc/fs/.../mb_stats to  disable statistics collection
>     * Write -1 to /proc/fs/.../mb_stats to clear statistics counters
> 
> And then deprecate the /sys/fs/.../mb_stats variable (but we probably
> won't be able to remove it for at least a year or two).
> 
> 	       	       	  	    	- Ted
Dear Ted, Baokun,
    Thank you for your review and suggestions.
    Since you mentioned that /sys/fs/.../mb_stats cannot be deleted in 
the short term,
    I plan to modify and submit a v4 patch according to the following 
strategy.

    1. Change `/proc/fs/.../mb_stats` to read-write mode.
	* Read `/proc/fs/.../mb_stats` to show statistics counters.
	* Write 0 to `/proc/fs/.../mb_stats` to disable statistics collection.
	* Write 1 to `/proc/fs/.../mb_stats` to enable statistics collection.
	* Write 2 to `/proc/fs/.../mb_stats` to clear statistics counters.

    2. Do not delete the `/sys/fs/.../mb_stats` node for now; implement 
the same write control logic.
	* Write 0 to `/sys/fs/.../mb_stats` to disable statistics collection.
	* Write 1 to `/sys/fs/.../mb_stats` to enable statistics collection.
	* Write 2 to `/sys/fs/.../mb_stats` to clear statistics counters.

	Delete `/sys/fs/.../mb_stats` later when it is possible to delete it.

    3. Modify the relevant documentation for `mb_stats`.
	Documentation/ABI/testing/sysfs-fs-ext4
	Documentation/admin-guide/ext4.rst
	Documentation/filesystems/proc.rst

    Compared to your suggestion, I recommend using the value 2 for the 
clear operation because s_mb_stats is an unsigned int variable, and 
using -1 requires changing the variable type.
    I suggest avoiding changing the s_mb_stats variable type unless 
absolutely necessary.

    Do you think this modification is appropriate?
    If there are no problems, I will start modifying the code and submit 
the v4 patch as soon as possible.

Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats

[Baokun Li]

On 2026/4/24 16:09, liubaolin wrote:
>
>
> 在 2026/4/24 0:19, Theodore Tso 写道:
>> On Wed, Apr 22, 2026 at 09:50:25AM +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.
>>
>> At the moment to enable mb_stats the system administrator needs to
>> write "1" to /sys/fs/ext4/<dev>/mb_stats, and writing "0" to the sysfs
>> file will pauce the statistics colleciton (but not clear the
>> statistics).  Adding a way to clear the statistics by writing to the
>> procfs file might be confusing to users.
>>
>> So.... as a suggestion, if you're adding to the ability to write to
>> /proc/fs/.../mb_stats, what if we make things work by
>>
>>     * Write 1 to /proc/fs/.../mb_stats to  enable statistics collection
>>     * Write 0 to /proc/fs/.../mb_stats to  disable statistics collection
>>     * Write -1 to /proc/fs/.../mb_stats to clear statistics counters
>>
>> And then deprecate the /sys/fs/.../mb_stats variable (but we probably
>> won't be able to remove it for at least a year or two).
>>
>>                                         - Ted
> Dear Ted, Baokun,
>    Thank you for your review and suggestions.
>    Since you mentioned that /sys/fs/.../mb_stats cannot be deleted in
> the short term,
>    I plan to modify and submit a v4 patch according to the following
> strategy.
>
>    1. Change `/proc/fs/.../mb_stats` to read-write mode.
>     * Read `/proc/fs/.../mb_stats` to show statistics counters.
>     * Write 0 to `/proc/fs/.../mb_stats` to disable statistics
> collection.
>     * Write 1 to `/proc/fs/.../mb_stats` to enable statistics collection.
>     * Write 2 to `/proc/fs/.../mb_stats` to clear statistics counters.
>
>    2. Do not delete the `/sys/fs/.../mb_stats` node for now; implement
> the same write control logic.
>     * Write 0 to `/sys/fs/.../mb_stats` to disable statistics collection.
>     * Write 1 to `/sys/fs/.../mb_stats` to enable statistics collection.
>     * Write 2 to `/sys/fs/.../mb_stats` to clear statistics counters.
>
>     Delete `/sys/fs/.../mb_stats` later when it is possible to delete it.
>
>    3. Modify the relevant documentation for `mb_stats`.
>     Documentation/ABI/testing/sysfs-fs-ext4
>     Documentation/admin-guide/ext4.rst
>     Documentation/filesystems/proc.rst
>
>    Compared to your suggestion, I recommend using the value 2 for the
> clear operation because s_mb_stats is an unsigned int variable, and
> using -1 requires changing the variable type.
>    I suggest avoiding changing the s_mb_stats variable type unless
> absolutely necessary.
>
>    Do you think this modification is appropriate?
>    If there are no problems, I will start modifying the code and
> submit the v4 patch as soon as possible.

For the clear command, we only handle it without storing it, so s_mb_stats
remains unchanged and still stores only 0 and non-zero values to represent
disabled and enabled, respectively. Otherwise, you will have to deal with
a large number of s_mb_stats checks

That means the /sys/fs/.../mb_stats interface does not need to support
clearing, but it might make sense to add a deprecation warning there.

Then in `/proc/fs/.../mb_stats`, writing 0 or a positive number passes
it to s_mb_stats, writing -1 performs a reset, and other negative values
return -EINVAL.


Cheers,
Baokun

Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats

[Theodore Tso]

On Fri, Apr 24, 2026 at 04:09:31PM +0800, liubaolin wrote:
> 
>    2. Do not delete the `/sys/fs/.../mb_stats` node for now; implement the
> same write control logic.
> 	* Write 0 to `/sys/fs/.../mb_stats` to disable statistics collection.
> 	* Write 1 to `/sys/fs/.../mb_stats` to enable statistics collection.
> 	* Write 2 to `/sys/fs/.../mb_stats` to clear statistics counters.

We could do that, but note that currently writing to
/sys/fs/.../mb_stats just sets an unsigned integer in
EXT4(sb)->s_mb_stats.  There is no ext4-specific function that runs
when /sys/fs/.../mb_stats is updated.

So either you have to add some check in fs/ext4/mballoc.c which gets
called every single time a block allocation happens --- and consider
the race condition where two CPU's are checking s_mb_stats at the same
time, and the desireability of adding a spinlock that would need to be
taken every single time a block allocation happens ---- or you have
add an ext4-specific function in fs/ext4/sysfs.c.

>    Compared to your suggestion, I recommend using the value 2 for the clear
> operation because s_mb_stats is an unsigned int variable, and using -1
> requires changing the variable type.

Well, since you have introduced an ext4-specific function which gets
called when writing to the procfs file, that function can clear the
statistics counter when -1 is written to the file --- and then set
s_mbi_stats to 1.

Cheers,

						- Ted