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
WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@techsingularity.net> To: Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com>, Yury Norov <yury.norov@gmail.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org, Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, David Rientjes <rientjes@google.com>, Vlastimil Babka <vbabka@suse.cz> 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-02-13 14:30 UTC|newest] Thread overview: 12+ 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 13:19 ` Mel Gorman 2019-02-13 13:20 ` Will Deacon 2019-02-13 13:20 ` Will Deacon 2019-02-13 13:42 ` Vlastimil Babka 2019-02-13 13:42 ` Vlastimil Babka 2019-02-13 14:15 ` Mel Gorman 2019-02-13 14:15 ` Mel Gorman 2019-02-13 14:30 ` Mel Gorman [this message] 2019-02-13 14:30 ` [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 Mel Gorman 2019-02-13 14:31 ` Vlastimil Babka 2019-02-13 14:31 ` Vlastimil Babka
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