On Tue 17-09-24 00:49:17, Frederic Weisbecker wrote:
> Kcompactd is dedicated to a specific node. As such it wants to be
> preferrably affine to it, memory and CPUs-wise.
>
> Use the proper kthread API to achieve that. As a bonus it takes care of
> CPU-hotplug events and CPU-isolation on its behalf.
>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Clear simplification, thanks!
> ---
> mm/compaction.c | 43 +++----------------------------------------
> 1 file changed, 3 insertions(+), 40 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index eb95e9b435d0..69742555f2e5 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -3179,15 +3179,9 @@ void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
> static int kcompactd(void *p)
> {
> pg_data_t *pgdat = (pg_data_t *)p;
> - struct task_struct *tsk = current;
> long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
> long timeout = default_timeout;
>
> - const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
> -
> - if (!cpumask_empty(cpumask))
> - set_cpus_allowed_ptr(tsk, cpumask);
> -
> set_freezable();
>
> pgdat->kcompactd_max_order = 0;
> @@ -3258,10 +3252,12 @@ void __meminit kcompactd_run(int nid)
> if (pgdat->kcompactd)
> return;
>
> - pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
> + pgdat->kcompactd = kthread_create_on_node(kcompactd, pgdat, nid, "kcompactd%d", nid);
> if (IS_ERR(pgdat->kcompactd)) {
> pr_err("Failed to start kcompactd on node %d\n", nid);
> pgdat->kcompactd = NULL;
> + } else {
> + wake_up_process(pgdat->kcompactd);
> }
> }
>
> @@ -3279,30 +3275,6 @@ void __meminit kcompactd_stop(int nid)
> }
> }
>
> -/*
> - * It's optimal to keep kcompactd on the same CPUs as their memory, but
> - * not required for correctness. So if the last cpu in a node goes
> - * away, we get changed to run anywhere: as the first one comes back,
> - * restore their cpu bindings.
> - */
> -static int kcompactd_cpu_online(unsigned int cpu)
> -{
> - int nid;
> -
> - for_each_node_state(nid, N_MEMORY) {
> - pg_data_t *pgdat = NODE_DATA(nid);
> - const struct cpumask *mask;
> -
> - mask = cpumask_of_node(pgdat->node_id);
> -
> - if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
> - /* One of our CPUs online: restore mask */
> - if (pgdat->kcompactd)
> - set_cpus_allowed_ptr(pgdat->kcompactd, mask);
> - }
> - return 0;
> -}
> -
> static int proc_dointvec_minmax_warn_RT_change(const struct ctl_table *table,
> int write, void *buffer, size_t *lenp, loff_t *ppos)
> {
> @@ -3362,15 +3334,6 @@ static struct ctl_table vm_compaction[] = {
> static int __init kcompactd_init(void)
> {
> int nid;
> - int ret;
> -
> - ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> - "mm/compaction:online",
> - kcompactd_cpu_online, NULL);
> - if (ret < 0) {
> - pr_err("kcompactd: failed to register hotplug callbacks.\n");
> - return ret;
> - }
>
> for_each_node_state(nid, N_MEMORY)
> kcompactd_run(nid);
> --
> 2.46.0
--
Michal Hocko
SUSE Labs
