Re: [patch v3 5/6] mm, thp: avoid excessive compaction latency during fault

[Mel Gorman]

On Tue, May 06, 2014 at 07:22:50PM -0700, David Rientjes wrote:
> Synchronous memory compaction can be very expensive: it can iterate an enormous 
> amount of memory without aborting, constantly rescheduling, waiting on page
> locks and lru_lock, etc, if a pageblock cannot be defragmented.
> 
> Unfortunately, it's too expensive for transparent hugepage page faults and 
> it's much better to simply fallback to pages.  On 128GB machines, we find that 
> synchronous memory compaction can take O(seconds) for a single thp fault.
> 
> Now that async compaction remembers where it left off without strictly relying
> on sync compaction, this makes thp allocations best-effort without causing
> egregious latency during fault.  We still need to retry async compaction after
> reclaim, but this won't stall for seconds.
> 
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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