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

[liubaolin <liubaolin12138@163.com>]

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.