From: Vlastimil Babka <vbabka@suse.cz> To: Mel Gorman <mgorman@techsingularity.net>, Andrew Morton <akpm@linux-foundation.org> Cc: Yury Norov <yury.norov@gmail.com>, 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: Re: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 Date: Wed, 13 Feb 2019 15:31:59 +0100 [thread overview] Message-ID: <7c0d323f-cad8-205b-5a8a-60da180a4ed0@suse.cz> (raw) In-Reply-To: <20190213143012.GT9565@techsingularity.net> On 2/13/19 3:30 PM, Mel Gorman wrote: > 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> Acked-by: Vlastimil Babka <vbabka@suse.cz> Thanks, sorry for the noise before. > --- > 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, >
WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz> To: Mel Gorman <mgorman@techsingularity.net>, 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, David Rientjes <rientjes@google.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 Date: Wed, 13 Feb 2019 15:31:59 +0100 [thread overview] Message-ID: <7c0d323f-cad8-205b-5a8a-60da180a4ed0@suse.cz> (raw) In-Reply-To: <20190213143012.GT9565@techsingularity.net> On 2/13/19 3:30 PM, Mel Gorman wrote: > 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> Acked-by: Vlastimil Babka <vbabka@suse.cz> Thanks, sorry for the noise before. > --- > 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, > _______________________________________________ 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 14:32 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 ` [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 Mel Gorman 2019-02-13 14:30 ` Mel Gorman 2019-02-13 14:31 ` Vlastimil Babka [this message] 2019-02-13 14:31 ` Vlastimil Babka
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