Re: [patch v3] mm, thp: only collapse hugepages to nodes with affinity for zone_reclaim_mode

[Vlastimil Babka]

On 07/17/2014 02:59 AM, David Rientjes wrote:
> Commit 9f1b868a13ac ("mm: thp: khugepaged: add policy for finding target
> node") improved the previous khugepaged logic which allocated a
> transparent hugepages from the node of the first page being collapsed.
>
> However, it is still possible to collapse pages to remote memory which may
> suffer from additional access latency.  With the current policy, it is
> possible that 255 pages (with PAGE_SHIFT == 12) will be collapsed remotely
> if the majority are allocated from that node.
>
> When zone_reclaim_mode is enabled, it means the VM should make every attempt
> to allocate locally to prevent NUMA performance degradation.  In this case,
> we do not want to collapse hugepages to remote nodes that would suffer from
> increased access latency.  Thus, when zone_reclaim_mode is enabled, only
> allow collapsing to nodes with RECLAIM_DISTANCE or less.
>
> There is no functional change for systems that disable zone_reclaim_mode.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

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