On Tue, Mar 24, 2020 at 06:11:17PM +0900, Jaewon Kim wrote:
> On 2020년 03월 23일 18:53, Greg KH wrote:
> >> +int register_meminfo_extra(atomic_long_t *val, int shift, const char 
> >> *name)
> >> +{
> >> +  struct meminfo_extra *meminfo, *memtemp;
> >> +  int len;
> >> +  int error = 0;
> >> +
> >> +  meminfo = kzalloc(sizeof(*meminfo), GFP_KERNEL);
> >> +  if (!meminfo) {
> >> +          error = -ENOMEM;
> >> +          goto out;
> >> +  }
> >> +
> >> +  meminfo->val = val;
> >> +  meminfo->shift_for_page = shift;
> >> +  strncpy(meminfo->name, name, NAME_SIZE);
> >> +  len = strlen(meminfo->name);
> >> +  meminfo->name[len] = ':';
> >> +  strncpy(meminfo->name_pad, meminfo->name, NAME_BUF_SIZE);
> >> +  while (++len < NAME_BUF_SIZE - 1)
> >> +          meminfo->name_pad[len] = ' ';
> >> +
> >> +  spin_lock(&meminfo_lock);
> >> +  list_for_each_entry_rcu(memtemp, &meminfo_head, list) {
> >> +          if (memtemp->val == val) {
> >> +                  error = -EINVAL;
> >> +                  break;
> >> +          }
> >> +  }
> >> +  if (!error)
> >> +          list_add_tail_rcu(&meminfo->list, &meminfo_head);
> >> +  spin_unlock(&meminfo_lock);
> > If you have a lock, why are you needing rcu?
> I think _rcu should be removed out of list_for_each_entry_rcu.
> But I'm confused about what you meant.
> I used rcu_read_lock on __meminfo_extra,
> and I think spin_lock is also needed for addition and deletion to handle 
> multiple modifiers.

If that's the case, then that's fine, it just didn't seem like that was
needed.  Or I might have been reading your rcu logic incorrectly...

> >> +  if (error)
> >> +          kfree(meminfo);
> >> +out:
> >> +
> >> +  return error;
> >> +}
> >> +EXPORT_SYMBOL(register_meminfo_extra);
> > EXPORT_SYMBOL_GPL()?  I have to ask :)
> I can use EXPORT_SYMBOL_GPL.
> >
> > thanks,
> >
> > greg k-h
> >
> >
> 
> Hello
> Thank you for your comment.
> 
> By the way there was not resolved discussion on v1 patch as I mentioned on 
> cover page.
> I'd like to hear your opinion on this /proc/meminfo_extra node.

I think it is the propagation of an old and obsolete interface that you
will have to support for the next 20+ years and yet not actually be
useful :)

> Do you think this is meaningful or cannot co-exist with other future
> sysfs based API.

What sysfs-based API?

I still don't know _why_ you want this.  The ION stuff is not needed as
that code is about to be deleted, so who else wants this?  What is the
use-case for it that is so desperately needed that parsing
yet-another-proc file is going to solve the problem?

thanks,

greg k-h

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