Re: [PATCH v2] mm/slub: don't wait for high-order page allocation

From: David Rientjes
Date: Wed Aug 12 2015 - 18:31:34 EST

On Fri, 7 Aug 2015, Joonsoo Kim wrote:

> Almost description is copied from commit fb05e7a89f50
> ("net: don't wait for order-3 page allocation").
> I saw excessive direct memory reclaim/compaction triggered by slub.
> This causes performance issues and add latency. Slub uses high-order
> allocation to reduce internal fragmentation and management overhead. But,
> direct memory reclaim/compaction has high overhead and the benefit of
> high-order allocation can't compensate the overhead of both work.
> This patch makes auxiliary high-order allocation atomic. If there is
> no memory pressure and memory isn't fragmented, the alloction will still
> success, so we don't sacrifice high-order allocation's benefit here.
> If the atomic allocation fails, direct memory reclaim/compaction will not
> be triggered, allocation fallback to low-order immediately, hence
> the direct memory reclaim/compaction overhead is avoided. In the
> allocation failure case, kswapd is waken up and trying to make high-order
> freepages, so allocation could success next time.
> Following is the test to measure effect of this patch.
> System: QEMU, CPU 8, 512 MB
> Mem: 25% memory is allocated at random position to make fragmentation.
> Memory-hogger occupies 150 MB memory.
> Workload: hackbench -g 20 -l 1000
> Average result by 10 runs (Base va Patched)
> elapsed_time(s): 4.3468 vs 2.9838
> compact_stall: 461.7 vs 73.6
> pgmigrate_success: 28315.9 vs 7256.1
> Signed-off-by: Joonsoo Kim <>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
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