From: Michal Hocko <mhocko@xxxxxxxx>
pagetypeinfo_showfree_print is called by zone->lock held in irq mode.
This is not really nice because it blocks both any interrupts on that
cpu and the page allocator. On large machines this might even trigger
the hard lockup detector.
Considering the pagetypeinfo is a debugging tool we do not really need
exact numbers here. The primary reason to look at the outuput is to see
how pageblocks are spread among different migratetypes therefore putting
a bound on the number of pages on the free_list sounds like a reasonable
tradeoff.
The new output will simply tell
[...]
Node 6, zone Normal, type Movable >100000 >100000 >100000 >100000 41019 31560 23996 10054 3229 983 648
instead of
Node 6, zone Normal, type Movable 399568 294127 221558 102119 41019 31560 23996 10054 3229 983 648
The limit has been chosen arbitrary and it is a subject of a future
change should there be a need for that.
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
mm/vmstat.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4e885ecd44d1..762034fc3b83 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1386,8 +1386,25 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
area = &(zone->free_area[order]);
- list_for_each(curr, &area->free_list[mtype])
+ list_for_each(curr, &area->free_list[mtype]) {
freecount++;
+ /*
+ * Cap the free_list iteration because it might
+ * be really large and we are under a spinlock
+ * so a long time spent here could trigger a
+ * hard lockup detector. Anyway this is a
+ * debugging tool so knowing there is a handful
+ * of pages in this order should be more than
+ * sufficient
+ */
+ if (freecount > 100000) {
+ seq_printf(m, ">%6lu ", freecount);
+ spin_unlock_irq(&zone->lock);
+ cond_resched();
+ spin_lock_irq(&zone->lock);
+ continue;
+ }
+ }
seq_printf(m, "%6lu ", freecount);
}
seq_putc(m, '\n');
--
2.20.1
