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由 Johannes Weiner 提交于
On NUMA systems, a node may start thrashing cache or even swap anonymous pages while there are still free pages on remote nodes. This is a result of commits 81c0a2bb ("mm: page_alloc: fair zone allocator policy") and fff4068c ("mm: page_alloc: revert NUMA aspect of fair allocation policy"). Before those changes, the allocator would first try all allowed zones, including those on remote nodes, before waking any kswapds. But now, the allocator fastpath doubles as the fairness pass, which in turn can only consider the local node to prevent remote spilling based on exhausted fairness batches alone. Remote nodes are only considered in the slowpath, after the kswapds are woken up. But if remote nodes still have free memory, kswapd should not be woken to rebalance the local node or it may thrash cash or swap prematurely. Fix this by adding one more unfair pass over the zonelist that is allowed to spill to remote nodes after the local fairness pass fails but before entering the slowpath and waking the kswapds. This also gets rid of the GFP_THISNODE exemption from the fairness protocol because the unfair pass is no longer tied to kswapd, which GFP_THISNODE is not allowed to wake up. However, because remote spills can be more frequent now - we prefer them over local kswapd reclaim - the allocation batches on remote nodes could underflow more heavily. When resetting the batches, use atomic_long_read() directly instead of zone_page_state() to calculate the delta as the latter filters negative counter values. Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org> Acked-by: NRik van Riel <riel@redhat.com> Acked-by: NMel Gorman <mgorman@suse.de> Cc: <stable@kernel.org> [3.12+] Signed-off-by: NAndrew Morton <akpm@linux-foundation.org> Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
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