Re: [PATCH] mm/ksm: prepare to remove the redundant ksm_merging_pages in procfs

[David Hildenbrand]

On 06.07.23 13:59, Nanyong Sun wrote:
> On 2023/7/6 16:55, David Hildenbrand wrote:
>
> > On 06.07.23 11:49, Nanyong Sun wrote:
> > > Since the ksm_merging_pages information already included in
> > > /proc/<pid>/ksm_stat, we could remove /proc/<pid>/ksm_merging_pages
> > > to make the directory more clean, and can save a little bit resources.
> > >
> > > To delete this interface more smoothly and avoid userspace break,
> > > retain this interface temporarily and modify its function to hint
> > > users to use ksm_stat instead.
> > >
> > > Signed-off-by: Nanyong Sun <sunnanyong@xxxxxxxxxx>
> > > ---
> > >    fs/proc/base.c | 9 +--------
> > >    1 file changed, 1 insertion(+), 8 deletions(-)
> > >
> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index eb2e498e3b8d..d080c58cbe6c 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -3189,14 +3189,7 @@ static int proc_pid_patch_state(struct
> > > seq_file *m, struct pid_namespace *ns,
> > >    static int proc_pid_ksm_merging_pages(struct seq_file *m, struct
> > > pid_namespace *ns,
> > >                    struct pid *pid, struct task_struct *task)
> > >    {
> > > -    struct mm_struct *mm;
> > > -
> > > -    mm = get_task_mm(task);
> > > -    if (mm) {
> > > -        seq_printf(m, "%lu\n", mm->ksm_merging_pages);
> > > -        mmput(mm);
> > > -    }
> > > -
> > > +    seq_puts(m, "please use /proc/<pid>/ksm_stat instead\n");
> > >        return 0;
> > >    }
> > >    static int proc_pid_ksm_stat(struct seq_file *m, struct
> > > pid_namespace *ns,
> >
> >
> > Why do we care so much about removing 15 simple LOC? That change here
> > will already mess with user space.
> >
> > Sorry, but IMHO it's all not worth the churn.
> We do not pay attention to these 15 LOC. We pay more attention to the
> redundant interface under procfs.
>
> This interface is used by developers and has a short history. Therefore,
> changing it now has no big impact.

Again, already 1 year old. And returning garbage instead of ripping it 
out might be even nastier.

--
Cheers,

David / dhildenb