Messages in this thread | | | Date | Thu, 20 Mar 2014 21:33:58 +0000 | From | Mel Gorman <> | Subject | Re: [patch] mm: page_alloc: spill to remote nodes before waking kswapd |
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On Thu, Mar 20, 2014 at 04:53:36PM -0400, Johannes Weiner wrote: > 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 81c0a2bb515f ("mm: page_alloc: fair zone allocator > policy") and fff4068cba48 ("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: Johannes Weiner <hannes@cmpxchg.org> > Cc: <stable@kernel.org> [3.12+]
Acked-by: Mel Gorman <mgorman@suse.de>
-- Mel Gorman SUSE Labs
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