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SubjectRe: [PATCH 1/9] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes
On Mon, Mar 06, 2017 at 10:37:40AM +0900, Minchan Kim wrote:
> On Fri, Mar 03, 2017 at 08:59:54AM +0100, Michal Hocko wrote:
> > On Fri 03-03-17 10:26:09, Minchan Kim wrote:
> > > On Tue, Feb 28, 2017 at 04:39:59PM -0500, Johannes Weiner wrote:
> > > > @@ -3316,6 +3325,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
> > > > sc.priority--;
> > > > } while (sc.priority >= 1);
> > > >
> > > > + if (!sc.nr_reclaimed)
> > > > + pgdat->kswapd_failures++;
> > >
> > > sc.nr_reclaimed is reset to zero in above big loop's beginning so most of time,
> > > it pgdat->kswapd_failures is increased.

That wasn't intentional; I didn't see the sc.nr_reclaimed reset.

---

From e126db716926ff353b35f3a6205bd5853e01877b Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@cmpxchg.org>
Date: Mon, 6 Mar 2017 10:53:59 -0500
Subject: [PATCH] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes fix

Check kswapd failure against the cumulative nr_reclaimed count, not
against the count from the lowest priority iteration.

Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
mm/vmscan.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ddcff8a11c1e..b834b2dd4e19 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3179,9 +3179,9 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
count_vm_event(PAGEOUTRUN);

do {
+ unsigned long nr_reclaimed = sc.nr_reclaimed;
bool raise_priority = true;

- sc.nr_reclaimed = 0;
sc.reclaim_idx = classzone_idx;

/*
@@ -3271,7 +3271,8 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages
*/
- if (raise_priority || !sc.nr_reclaimed)
+ nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
+ if (raise_priority || !nr_reclaimed)
sc.priority--;
} while (sc.priority >= 1);

--
2.11.1
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