On Mon, Jan 22, 2024 at 04:03:53PM +0800, Huang, Ying wrote:
> Gregory Price <gourry.memverge@xxxxxxxxx> writes:
>
> > + /*
> > + * The default weight is 1 (for now), when the kernel-internal
> > + * default weight array is implemented, this should be updated to
> > + * collect the system-default weight of the node if the user passes 0.
> > + */
> > + if (!weight)
> > + weight = 1;
>
> From functionality point of view, it's OK to set "weight = 1" here now.
> But when we add system default weight table in the future, we need to
> use "weight = 0". Otherwise, we cannot distinguish whether the default
> value have been customized via sysfs. So, I suggest to use that rule.
>
[... snip ...]
> > + else
> > + memset(new, 1, nr_node_ids);
>
> With similar reason as above ("From functionality..."), I suggest to set
> "0" here.
>
blah - the comment is misleading at best. The future patch should pass
0 through to the sysfs table and the allocators updated to collect the
system-default weight of the node.
re: doing it this way right now -
I chose to do it this way for now because it ultimately simplifies the
logic in the allocators - all of which will need to be updated with the
future patch set regardless of our implementation choice now.
e.g.
rcu_read_lock();
table = rcu_dereference(iw_table);
if (!policy->wil.cur_weight)
policy->wil.cur_weight = table ? table[next] : 1;
^^^ only need single conditional now
rcu_read_unlock();
This logic will need to be updated to use default table values, so I
chose the simpler implementation and left the change to be explicit
at the time the default table is implemented.
If you prefer it the other way now, I can change it, but this seemed
cleaner and simpler for the time being.
> > + new[node_attr->nid] = weight;
> > + rcu_assign_pointer(iw_table, new);
> > + mutex_unlock(&iw_table_lock);
> > + synchronize_rcu();
> > + kfree(old);
> > + return count;
> > +}
> > +
> > +static struct iw_node_attr *node_attrs[MAX_NUMNODES];
>
> node_attrs[] can be allocated dynamically too. Just a suggestion.
>
ack to this and other references to nr_node_ids, will change.
> > + kfree(old);
>
> It appears unnecessary to free iw_table in error path. But this isn't a
> big deal because error path will almost never be executed in practice.
>
checkpatch.pl yells at you if you do null checks before kfree :]
> > + int err;
> > + struct kobject *mempolicy_kobj;
>
> This overrides the global "mempolicy_kobj" defined before function. But
> I don't think we need the global definition.
>
Assuming the exit path isn't needed then yeah the global isn't needed.
> > +static int __init mempolicy_sysfs_init(void)
> > +{
> > + /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
> > + iw_table = NULL;
> > + return 0;
> > +}
> > +
> > +static void __exit mempolicy_exit(void) { }
> > +#endif /* CONFIG_SYSFS */
> > +late_initcall(mempolicy_sysfs_init);
> > +module_exit(mempolicy_exit);
>
> mempolicy.c will not be compiled as module, so we don't need
> module_exit().
>
ack
