| Message ID | 20190213143012.GT9565@techsingularity.net (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Commit | 94b3334cbebea34d56a7e6321c6fe9d89b309a49 |
| Headers | show |
| Series | mm, page_alloc: Fix a division by zero error when boosting watermarks v2 | expand |
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, >
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,
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(+)