Messages in this thread | | | Subject | Re: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced | From | Shaohua Li <> | Date | Wed, 01 Dec 2010 10:13:56 +0800 |
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On Wed, 2010-12-01 at 01:15 +0800, Mel Gorman wrote: > When the allocator enters its slow path, kswapd is woken up to balance the > node. It continues working until all zones within the node are balanced. For > order-0 allocations, this makes perfect sense but for higher orders it can > have unintended side-effects. If the zone sizes are imbalanced, kswapd > may reclaim heavily on a smaller zone discarding an excessive number of > pages. The user-visible behaviour is that kswapd is awake and reclaiming > even though plenty of pages are free from a suitable zone. > > This patch alters the "balance" logic to stop kswapd if any suitable zone > becomes balanced to reduce the number of pages it reclaims from other zones. from my understanding, the patch will break reclaim high zone if a low zone meets the high order allocation, even the high zone doesn't meet the high order allocation. This, for example, will make a high order allocation from a high zone fallback to low zone and quickly exhaust low zone, for example DMA. This will break some drivers.
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