mm: Create/affine kcompactd to its preferred node

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@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index a2b16b08cbbff70c1decefb357c5523d8483fbac..a31c0f5758cfa0bb9c22fac45bdbf9605b13df02 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -3154,15 +3154,9 @@ 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;
@@ -3233,10 +3227,12 @@ 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);
        }
 }
 
@@ -3254,30 +3250,6 @@ 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)
 {
@@ -3337,15 +3309,6 @@ 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);