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mm, page_alloc: fix a division by zero error when boosting watermarks v2

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Yury Norov reported that an arm64 KVM instance could not boot since
after v5.0-rc1 and could addressed by reverting the patches

  1c30844d2d ("mm: reclaim small amounts of memory when an external
  73444bc4d8 ("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/[email protected]
Fixes: 1c30844d2d ("mm: reclaim small amounts of memory when an external fragmentation event occurs")
Signed-off-by: Mel Gorman <[email protected]>
Reported-by: Yury Norov <[email protected]>
Tested-by: Yury Norov <[email protected]>
Tested-by: Will Deacon <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Catalin Marinas <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Mel Gorman 2019-02-20 22:19:49 -08:00 • committed by Linus Torvalds
commit 94b3334cbe
1 changed files with 12 additions and 0 deletions
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12
mm/page_alloc.c
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@ -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,