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
