linux-kernel - Re: [PATCH 1/9] mm: fix 100% CPU kswapd busyloop on unreclaimable nodes

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Date:   Mon, 6 Mar 2017 11:24:10 -0500
From:   Johannes Weiner <hannes@...xchg.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jia He <hejianet@...il.com>, Mel Gorman <mgorman@...e.de>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [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@...xchg.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@...nel.org>
Signed-off-by: Johannes Weiner <hannes@...xchg.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