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authorMel Gorman <mgorman@techsingularity.net>2019-02-20 22:19:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-02-21 09:01:00 -0800
commit94b3334cbebea34d56a7e6321c6fe9d89b309a49 (patch)
tree594051108f28d96925d28f169933ade8b23cad9d
parent311ade0eab192f0abee2f70bce761bf0d66990c4 (diff)
mm, page_alloc: fix a division by zero error when boosting watermarks v2
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. Link: http://lkml.kernel.org/r/20190213143012.GT9565@techsingularity.net Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Reported-by: Yury Norov <yury.norov@gmail.com> Tested-by: Yury Norov <yury.norov@gmail.com> Tested-by: Will Deacon <will.deacon@arm.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/page_alloc.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7f79b78bc829..0b9f577b1a2a 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,