Re: [PATCH v3 v3 2/2] ext4: allow clearing mballoc stats through mb_stats
From: liubaolin
Date: Fri Apr 24 2026 - 04:12:00 EST
在 2026/4/24 0:19, Theodore Tso 写道:
On Wed, Apr 22, 2026 at 09:50:25AM +0800, Baolin Liu wrote:Dear Ted, Baokun,
From: Baolin Liu <liubaolin@xxxxxxxxxx>
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
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.