Re: [PATCH v2 3/5] mm: demotion: Add support to set targets from userspace

[Wei Xu <weixugc@google.com>]

On Wed, Apr 13, 2022 at 2:22 AM Jagdish Gediya <jvgediya@linux.ibm.com> wrote:
>
> Add support to set node_states[N_DEMOTION_TARGETS] from
> user space to override the default demotion targets.
>
> Restrict demotion targets to memory only numa nodes
> while setting them from user space.
>
> Demotion targets can be set from userspace using command,
> echo <nodelist> > /sys/kernel/mm/numa/demotion_target
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
> ---
>  .../ABI/testing/sysfs-kernel-mm-numa          | 12 +++++++
>  mm/migrate.c                                  | 35 +++++++++++++++++++
>  2 files changed, 47 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-numa b/Documentation/ABI/testing/sysfs-kernel-mm-numa
> index 77e559d4ed80..10e9e643845c 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-mm-numa
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-numa
> @@ -22,3 +22,15 @@ Description: Enable/disable demoting pages during reclaim
>                 the guarantees of cpusets.  This should not be enabled
>                 on systems which need strict cpuset location
>                 guarantees.
> +
> +What:          /sys/kernel/mm/numa/demotion_target

demotion_target -> demotion_targets?

Also, with the previous change, we already have
/sys/devices/system/node/has_demotion_targets (or demotion_targets as
I have suggested). Wouldn't it be simpler to make that sysfs file
writable instead of adding a parallel interface?

> +Date:          April 2022
> +Contact:       Linux memory management mailing list <linux-mm@kvack.org>
> +Description:   Configure demotion target nodes
> +
> +               Page migration during reclaim is intended for systems
> +               with tiered memory configurations. Preferred migration target
> +               nodes can be configured in a system using this interface, based
> +               on which demotion table is prepared in kernel. If demotion is
> +               enabled then pages will be migrated to set demotion targets
> +               during reclaim.
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 516f4e1348c1..4d3d80ca0a7f 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2564,12 +2564,47 @@ static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
>         return count;
>  }
>
> +
> +static ssize_t numa_demotion_target_show(struct kobject *kobj,
> +                                         struct kobj_attribute *attr, char *buf)
> +{
> +       return sysfs_emit(buf, "%*pbl\n",
> +                         nodemask_pr_args(&node_states[N_DEMOTION_TARGETS]));
> +}
> +
> +static ssize_t numa_demotion_target_store(struct kobject *kobj,
> +                                         struct kobj_attribute *attr,
> +                                         const char *nodelist, size_t count)
> +{
> +       nodemask_t nodes;
> +
> +       if (nodelist_parse(nodelist, nodes))
> +               return -EINVAL;
> +
> +       if (!nodes_subset(nodes, node_states[N_MEMORY]))
> +               return -EINVAL;
> +
> +       if (nodes_intersects(nodes, node_states[N_CPU]))
> +               return -EINVAL;
> +
> +       node_states[N_DEMOTION_TARGETS] = nodes;
> +
> +       set_migration_target_nodes();
> +
> +       return count;
> +}
> +
>  static struct kobj_attribute numa_demotion_enabled_attr =
>         __ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
>                numa_demotion_enabled_store);
>
> +static struct kobj_attribute numa_demotion_target_attr =
> +       __ATTR(demotion_target, 0644, numa_demotion_target_show,
> +              numa_demotion_target_store);
> +
>  static struct attribute *numa_attrs[] = {
>         &numa_demotion_enabled_attr.attr,
> +       &numa_demotion_target_attr.attr,
>         NULL,
>  };
>
> --
> 2.35.1
>
>