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mm: disable zone_reclaim_mode by default · torvalds/linux@4f9b16a · GitHub
source link: https://github.com/torvalds/linux/commit/4f9b16a64753d0bb607454347036dc997fd03b82
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disable zone_reclaim_mode by default · torvalds/linux@4f9b16a · GitHub Permalink
mm: disable zone_reclaim_mode by default
When it was introduced, zone_reclaim_mode made sense as NUMA distances punished and workloads were generally partitioned to fit into a NUMA node. NUMA machines are now common but few of the workloads are NUMA-aware and it's routine to see major performance degradation due to zone_reclaim_mode being enabled but relatively few can identify the problem. Those that require zone_reclaim_mode are likely to be able to detect when it needs to be enabled and tune appropriately so lets have a sensible default for the bulk of users. This patch (of 2): zone_reclaim_mode causes processes to prefer reclaiming memory from local node instead of spilling over to other nodes. This made sense initially when NUMA machines were almost exclusively HPC and the workload was partitioned into nodes. The NUMA penalties were sufficiently high to justify reclaiming the memory. On current machines and workloads it is often the case that zone_reclaim_mode destroys performance but not all users know how to detect this. Favour the common case and disable it by default. Users that are sophisticated enough to know they need zone_reclaim_mode will detect it. Signed-off-by: Mel Gorman <[email protected]> Acked-by: Johannes Weiner <[email protected]> Reviewed-by: Zhang Yanfei <[email protected]> Acked-by: Michal Hocko <[email protected]> Reviewed-by: Christoph Lameter <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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