From 1ce7d3cedb9c12b3f0015667f505cff6588e142f Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Tue, 5 Nov 2019 21:16:44 -0800
Subject: [PATCH 1/1] mm, vmstat: reduce zone->lock holding time by
/proc/pagetypeinfo
Git-commit: 93b3a674485f6a4b8ffff85d1682d5e8b7c51560
Patch-mainline: v5.4-rc7
References: bsc#1175691
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 and low number of
pages is much more interesting 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.
While we are at it, also drop the zone lock after each free_list
iteration which will help with the IRQ and page allocator responsiveness
even further as the IRQ lock held time is always bound to those 100k
pages.
[akpm@linux-foundation.org: tweak comment text, per David Hildenbrand]
Link: http://lkml.kernel.org/r/20191025072610.18526-3-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Rafael Aquini <aquini@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Roman Gushchin <guro@fb.com>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Firo Yang <firo.yang@suse.com>
---
mm/vmstat.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index e00c6067e27e..8a6bf3288926 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1368,12 +1368,29 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
unsigned long freecount = 0;
struct free_area *area;
struct list_head *curr;
+ bool overflow = false;
area = &(zone->free_area[order]);
- list_for_each(curr, &area->free_list[mtype])
- freecount++;
- seq_printf(m, "%6lu ", freecount);
+ list_for_each(curr, &area->free_list[mtype]) {
+ /*
+ * 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 of this order should be more than
+ * sufficient.
+ */
+ if (++freecount >= 100000) {
+ overflow = true;
+ break;
+ }
+ }
+ seq_printf(m, "%s%6lu ", overflow ? ">" : "", freecount);
+ spin_unlock_irq(&zone->lock);
+ cond_resched();
+ spin_lock_irq(&zone->lock);
}
seq_putc(m, '\n');
}
--
2.16.4