On Tue, Mar 24, 2020 at 06:11:17PM +0900, Jaewon Kim wrote:

On 2020년 03월 23일 18:53, Greg KH wrote:

quoted

quoted

+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...

quoted

quoted

+	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.

quoted

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