Remote draining of pages was removed from 5.6-rt.
Unfortunately its necessary for use-cases which have a busy spinning
SCHED_FIFO thread on isolated CPU:
[ 7475.821066] INFO: task ld:274531 blocked for more than 600 seconds.
[ 7475.822157] Not tainted 4.18.0-208.rt5.20.el8.x86_64 #1
[ 7475.823094] echo 0 /proc/sys/kernel/hung_task_timeout_secs disables this message.
[ 7475.824392] ld D 0 274531 274530 0x00084080
[ 7475.825307] Call Trace:
[ 7475.825761] __schedule+0x342/0x850
[ 7475.826377] schedule+0x39/0xd0
[ 7475.826923] schedule_timeout+0x20e/0x410
[ 7475.827610] ? __schedule+0x34a/0x850
[ 7475.828247] ? ___preempt_schedule+0x16/0x18
[ 7475.828953] wait_for_completion+0x85/0xe0
[ 7475.829653] flush_work+0x11a/0x1c0
[ 7475.830313] ? flush_workqueue_prep_pwqs+0x130/0x130
[ 7475.831148] drain_all_pages+0x140/0x190
[ 7475.831803] __alloc_pages_slowpath+0x3f8/0xe20
[ 7475.832571] ? mem_cgroup_commit_charge+0xcb/0x510
[ 7475.833371] __alloc_pages_nodemask+0x1ca/0x2b0
[ 7475.834134] pagecache_get_page+0xb5/0x2d0
[ 7475.834814] ? account_page_dirtied+0x11a/0x220
[ 7475.835579] grab_cache_page_write_begin+0x1f/0x40
[ 7475.836379] iomap_write_begin.constprop.44+0x1c1/0x370
[ 7475.837241] ? iomap_write_end+0x91/0x290
[ 7475.837911] iomap_write_actor+0x92/0x170
...
So enable remote draining again.
The original commit message is:
mm: page_alloc: rt-friendly per-cpu pages
rt-friendly per-cpu pages: convert the irqs-off per-cpu locking
method into a preemptible, explicit-per-cpu-locks method.
Contains fixes from:
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Thomas Gleixner <tglx@xxxxxxxxxxxxx>
From: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
---
mm/page_alloc.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
Index: linux-rt-devel/mm/page_alloc.c
===================================================================
--- linux-rt-devel.orig/mm/page_alloc.c
+++ linux-rt-devel/mm/page_alloc.c
@@ -360,6 +360,16 @@ EXPORT_SYMBOL(nr_online_nodes);
static DEFINE_LOCAL_IRQ_LOCK(pa_lock);
+#ifdef CONFIG_PREEMPT_RT
+# define cpu_lock_irqsave(cpu, flags) \
+ local_lock_irqsave_on(pa_lock, flags, cpu)
+# define cpu_unlock_irqrestore(cpu, flags) \
+ local_unlock_irqrestore_on(pa_lock, flags, cpu)
+#else
+# define cpu_lock_irqsave(cpu, flags) local_irq_save(flags)
+# define cpu_unlock_irqrestore(cpu, flags) local_irq_restore(flags)
+#endif
+
int page_group_by_mobility_disabled __read_mostly;
#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
@@ -2852,7 +2862,7 @@ static void drain_pages_zone(unsigned in
LIST_HEAD(dst);
int count;
- local_lock_irqsave(pa_lock, flags);
+ cpu_lock_irqsave(cpu, flags);
pset = per_cpu_ptr(zone->pageset, cpu);
pcp = &pset->pcp;
@@ -2860,7 +2870,7 @@ static void drain_pages_zone(unsigned in
if (count)
isolate_pcp_pages(count, pcp, &dst);
- local_unlock_irqrestore(pa_lock, flags);
+ cpu_unlock_irqrestore(cpu, flags);
if (count)
free_pcppages_bulk(zone, &dst, false);
@@ -2898,6 +2908,7 @@ void drain_local_pages(struct zone *zone
drain_pages(cpu);
}
+#ifndef CONFIG_PREEMPT_RT
static void drain_local_pages_wq(struct work_struct *work)
{
struct pcpu_drain *drain;
@@ -2915,6 +2926,7 @@ static void drain_local_pages_wq(struct
drain_local_pages(drain->zone);
migrate_enable();
}
+#endif
/*
* Spill all the per-cpu pages from all CPUs back into the buddy allocator.
@@ -2982,6 +2994,7 @@ void drain_all_pages(struct zone *zone)
cpumask_clear_cpu(cpu, &cpus_with_pcps);
}
+#ifndef CONFIG_PREEMPT_RT
for_each_cpu(cpu, &cpus_with_pcps) {
struct pcpu_drain *drain = per_cpu_ptr(&pcpu_drain, cpu);
@@ -2991,6 +3004,10 @@ void drain_all_pages(struct zone *zone)
}
for_each_cpu(cpu, &cpus_with_pcps)
flush_work(&per_cpu_ptr(&pcpu_drain, cpu)->work);
+#else
+ for_each_cpu(cpu, &cpus_with_pcps)
+ drain_pages(cpu);
+#endif
mutex_unlock(&pcpu_drain_mutex);
}
