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    SubjectRe: [PATCH 1/3] mm: kswapd: Stop high-order balancing when any suitable zone is balanced
    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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      Last update: 2010-12-01 03:17    [W:0.019 / U:35.172 seconds]
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