Re: [PATCH v6 03/13] mm/demotion: Return error on write to numa_demotion sysfs

Ying Huang
2022-06-14T08:42:23Z

On Mon, 2022-06-13 at 11:18 +0530, Aneesh Kumar K V wrote:
> On 6/13/22 11:03 AM, Ying Huang wrote:
> > On Mon, 2022-06-13 at 09:05 +0530, Aneesh Kumar K V wrote:
> > > On 6/13/22 8:56 AM, Ying Huang wrote:
> > > > On Fri, 2022-06-10 at 19:22 +0530, Aneesh Kumar K.V wrote:
> > > > > With CONFIG_MIGRATION disabled return EINVAL on write.
> > > > >
> > > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> > > > > ---
> > > > >    mm/memory-tiers.c | 3 +++
> > > > >    1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
> > > > > index 9c6b40d7e0bf..c3123a457d90 100644
> > > > > --- a/mm/memory-tiers.c
> > > > > +++ b/mm/memory-tiers.c
> > > > > @@ -105,6 +105,9 @@ static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
> > > > >    {
> > > > >     ssize_t ret;
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > + if (!IS_ENABLED(CONFIG_MIGRATION))
> > > > > + return -EINVAL;
> > > > > +
> > > >
> > > > How about enclose numa_demotion_enabled_xxx related code with CONFIG_MIGRATION?
> > > >
> > >
> > > IIUC there is a desire to use IS_ENABLED() in the kernel instead of
> > > #ifdef since that helps in more compile time checks. Because there are
> > > no dead codes during compile now with IS_ENABLED().
> >
> > IS_ENABLED() is used to reduce usage of "#ifdef" in ".c" file,
> > especially inside a function. We have good build test coverage with
> > 0Day now.
> >
> > To avoid code size inflate, it's better to use #ifdef CONFIG_MIGRATION.
> >
>
> For a diff like below I am finding IS_ENABLED better.
>
> size memory-tiers.o.isenabled memory-tiers.o
>     text data bss dec hex filename
>     4776 989 5 5770 168a memory-tiers.o.isenabled
>     5257 990 5 6252 186c memory-tiers.o
>
>
> modified mm/memory-tiers.c
> @@ -710,12 +710,11 @@ static int __meminit
> migrate_on_reclaim_callback(struct notifier_block *self,
>
>   static void __init migrate_on_reclaim_init(void)
>   {
> -
> - if (IS_ENABLED(CONFIG_MIGRATION)) {
> +#ifdef CONFIG_MIGRATION
>    node_demotion = kcalloc(MAX_NUMNODES, sizeof(struct demotion_nodes),
>    GFP_KERNEL);
>    WARN_ON(!node_demotion);
> - }
> +#endif
>    hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
>   }
>
> @@ -844,14 +843,19 @@ static ssize_t numa_demotion_enabled_show(struct
> kobject *kobj,
>    numa_demotion_enabled ? "true" : "false");
>   }
>
> +#ifdef CONFIG_MIGRATION
>   static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
>    struct kobj_attribute *attr,
>    const char *buf, size_t count)
>   {
> - ssize_t ret;
> -
> - if (!IS_ENABLED(CONFIG_MIGRATION))
> - return -EINVAL;
> + return -EINVAL;
> +}
> +#else
> +static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + ssize_t ret;
>
>    ret = kstrtobool(buf, &numa_demotion_enabled);
>    if (ret)
> @@ -859,6 +863,7 @@ static ssize_t numa_demotion_enabled_store(struct
> kobject *kobj,
>
>    return count;
>   }
> +#endif
>
>   static struct kobj_attribute numa_demotion_enabled_attr =
>    __ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
>
> I also find that #ifdef config not easier to the eyes. If there is a
> large code that we can end up #ifdef out, then it might be worth it.
> IIUC, we might want to keep the establish_migration target to find
> top_tier rank and lower_tier mask. Once we do that only thing that we
> could comment out is the node_demotion sysfs creation and I was
> considering to keep that even if migration is disabled with a write to
> the file returning EINVAL. I could switch that if you strongly feel that
> we should hide node_demotion sysfs file.

Per my understanding, we can enclose most code about
demoting/promoting inside CONFIG_MIGRATION, including
numa/demotion_enabled sysfs interface. In this way, the code size can
be reduced.

Best Regards,
Huang, Ying