linux-kernel - Re: [lkp-robot] [mm] aefd950b83: divide

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Message-Id: <20170531135226.0a1b403a7a4e3f76f8f9d6bc@linux-foundation.org>
Date:   Wed, 31 May 2017 13:52:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     Josef Bacik <josef@...icpanda.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Josef Bacik <jbacik@...com>, Rik van Riel <riel@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [lkp-robot] [mm]  aefd950b83: divide_error:#[##]

On Wed, 31 May 2017 14:31:16 +0800 kernel test robot <xiaolong.ye@...el.com> wrote:

> 
> FYI, we noticed the following commit:
> 
> commit: aefd950b83d2d8cf4d3c270546c8725f866da191 ("mm: make kswapd try harder to keep active pages in cache")
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> 
> in testcase: boot
> 
> ...
>
> [  160.541829] divide error: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>
> ...
>
> [  160.587334] RIP: shrink_node+0x47f/0x5a0 RSP: ffffc900001bbd78
>
> ...


hm.  This?

--- a/mm/vmscan.c~mm-make-kswapd-try-harder-to-keep-active-pages-in-cache-fix-2
+++ a/mm/vmscan.c
@@ -2724,7 +2724,7 @@ static bool shrink_node(pg_data_t *pgdat
 		if (sc->nr_reclaimed - nr_reclaimed) {
 			reclaimable = true;
 		} else if (sc->inactive_only && !skip_slab) {
-			unsigned long percent;
+			unsigned long percent = 100;
 
 			/*
 			 * We didn't reclaim anything this go around, so the
@@ -2735,7 +2735,8 @@ static bool shrink_node(pg_data_t *pgdat
 			 * hoping that eventually we'll start freeing enough
 			 * objects to reclaim space.
 			 */
-			percent = (slab_reclaimed * 100 / slab_scanned);
+			if (slab_scanned)
+				percent = (slab_reclaimed * 100 / slab_scanned);
 			if (percent < 50)
 				sc->inactive_only = 0;
 			else

Or this?

--- a/mm/vmscan.c~mm-make-kswapd-try-harder-to-keep-active-pages-in-cache-fix-3
+++ a/mm/vmscan.c
@@ -2628,7 +2628,7 @@ static bool shrink_node(pg_data_t *pgdat
 		};
 		unsigned long node_lru_pages = 0;
 		unsigned long slab_reclaimed = 0;
-		unsigned long slab_scanned = 0;
+		unsigned long slab_scanned = 1;		/* Avoid div-by-zero */
 		struct mem_cgroup *memcg;
 
 		nr_reclaimed = sc->nr_reclaimed;
_