From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Yury Norov <yury.norov@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
Andrea Arcangeli <aarcange@redhat.com>,
David Rientjes <rientjes@google.com>,
Michal Hocko <mhocko@kernel.org>,
Will Deacon <will.deacon@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org
Subject: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2
Date: Wed, 13 Feb 2019 14:30:13 +0000 [thread overview]
Message-ID: <20190213143012.GT9565@techsingularity.net> (raw)
In-Reply-To: <20190213131923.GQ9565@techsingularity.net>
Yury Norov reported that an arm64 KVM instance could not boot since after
v5.0-rc1 and could addressed by reverting the patches
1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external
73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held")
The problem is that a division by zero error is possible if boosting
occurs very early in boot if the system has very little memory. This
patch avoids the division by zero error.
Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs")
Reported-and-tested-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d295c9bc01a8..bb1c7d843ebf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2170,6 +2170,18 @@ static inline void boost_watermark(struct zone *zone)
max_boost = mult_frac(zone->_watermark[WMARK_HIGH],
watermark_boost_factor, 10000);
+
+ /*
+ * high watermark may be uninitialised if fragmentation occurs
+ * very early in boot so do not boost. We do not fall
+ * through and boost by pageblock_nr_pages as failing
+ * allocations that early means that reclaim is not going
+ * to help and it may even be impossible to reclaim the
+ * boosted watermark resulting in a hang.
+ */
+ if (!max_boost)
+ return;
+
max_boost = max(pageblock_nr_pages, max_boost);
zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages,
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2019-02-13 14:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-13 13:19 [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks Mel Gorman
2019-02-13 13:20 ` Will Deacon
2019-02-13 13:42 ` Vlastimil Babka
2019-02-13 14:15 ` Mel Gorman
2019-02-13 14:30 ` Mel Gorman [this message]
2019-02-13 14:31 ` [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 Vlastimil Babka
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