The patch titled
Subject: mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo
has been added to the -mm tree. Its filename is
mm-vmstat-reduce-zone-lock-holding-time-by-proc-pagetypeinfo.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-vmstat-reduce-zone-lock-holding-time-by-proc-pagetypeinfo.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-vmstat-reduce-zone-lock-holding-time-by-proc-pagetypeinfo.patch
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From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm, vmstat: reduce zone->lock holding time by /proc/pagetypeinfo
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.
Link: http://lkml.kernel.org/r/20191025072610.18526-3-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Rafael Aquini <aquini@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
--- a/mm/vmstat.c~mm-vmstat-reduce-zone-lock-holding-time-by-proc-pagetypeinfo
+++ a/mm/vmstat.c
@@ -1383,12 +1383,29 @@ static void pagetypeinfo_showfree_print(
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 in 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');
}
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-vmstat-hide-proc-pagetypeinfo-from-normal-users.patch
mm-vmstat-reduce-zone-lock-holding-time-by-proc-pagetypeinfo.patch
