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

[liubaolin]

Dear Baokun,
   Thank you and Ted for your review and suggestions.
   I will incorporate your suggestions and submit the v4 patch as soon 
as possible.

Thanks,
Baolin

在 2026/4/24 17:34, Baokun Li 写道:
> 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@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
> > 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