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

[liubaolin <liubaolin12138@163.com>]

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
>>