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Date: Tue, 02 Sep 2014 10:12:59 +0900
From: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Mel Gorman <mgorman@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>
CC: Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
David Rientjes <rientjes@...gle.com>,
Fengguang Wu <fengguang.wu@...el.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: Default to node-ordering on 64-bit NUMA
machines
(2014/09/01 21:55), Mel Gorman wrote:
> Zones are allocated by the page allocator in either node or zone order.
> Node ordering is preferred in terms of locality and is applied automatically
> in one of three cases.
>
> 1. If a node has only low memory
>
> 2. If DMA/DMA32 is a high percentage of memory
>
> 3. If low memory on a single node is greater than 70% of the node size
>
> Otherwise zone ordering is used to preserve low memory. Unfortunately
> a consequence of this is that a machine with balanced NUMA nodes will
> experience different performance characteristics depending on which node
> they happen to start from.
>
> The point of zone ordering is to protect lower nodes for devices that require
> DMA/DMA32 memory. When NUMA was first introduced, this was critical as 32-bit
> NUMA machines commonly suffered from low memory exhaustion problems. On
> 64-bit machines the primary concern is devices that are 32-bit only which
> is less severe than the low memory exhaustion problem on 32-bit NUMA. It
> seems there are really few devices that depends on it.
>
> AGP -- I assume this is getting more rare but even then I think the allocations
> happen early in boot time where lowmem pressure is less of a problem
>
> DRM -- If the device is 32-bit only then there may be low pressure. I didn't
> evaluate these in detail but it looks like some of these are mobile
> graphics card. Not many NUMA laptops out there. DRM folk should know
> better though.
>
> Some TV cards -- Much demand for 32-bit capable TV cards on NUMA machines?
>
> B43 wireless card -- again not really a NUMA thing.
>
> I cannot find a good reason to incur a performance penalty on all 64-bit NUMA
> machines in case someone throws a brain damanged TV or graphics card in there.
> This patch defaults to node-ordering on 64-bit NUMA machines. I was tempted
> to make it default everywhere but I understand that some embedded arches may
> be using 32-bit NUMA where I cannot predict the consequences.
>
> The performance impact depends on the workload and the characteristics of the
> machine and the machine I tested on had a large Normal zone on node 0 so the
> impact is within the noise for the majority of tests. The allocation stats
> show more allocation requests were from DMA32 and local node. Running SpecJBB
> with multiple JVMs and automatic NUMA balancing disabled the results were
>
> specjbb
> 3.17.0-rc2 3.17.0-rc2
> vanilla nodeorder-v1r1
> Min 1 29534.00 ( 0.00%) 30020.00 ( 1.65%)
> Min 10 115717.00 ( 0.00%) 134038.00 ( 15.83%)
> Min 19 109718.00 ( 0.00%) 114186.00 ( 4.07%)
> Min 28 104459.00 ( 0.00%) 103639.00 ( -0.78%)
> Min 37 98245.00 ( 0.00%) 103756.00 ( 5.61%)
> Min 46 97198.00 ( 0.00%) 96197.00 ( -1.03%)
> Mean 1 30953.25 ( 0.00%) 31917.75 ( 3.12%)
> Mean 10 124432.50 ( 0.00%) 140904.00 ( 13.24%)
> Mean 19 116033.50 ( 0.00%) 119294.75 ( 2.81%)
> Mean 28 108365.25 ( 0.00%) 106879.50 ( -1.37%)
> Mean 37 102984.75 ( 0.00%) 106924.25 ( 3.83%)
> Mean 46 100783.25 ( 0.00%) 105368.50 ( 4.55%)
> Stddev 1 1260.38 ( 0.00%) 1109.66 ( 11.96%)
> Stddev 10 7434.03 ( 0.00%) 5171.91 ( 30.43%)
> Stddev 19 8453.84 ( 0.00%) 5309.59 ( 37.19%)
> Stddev 28 4184.55 ( 0.00%) 2906.63 ( 30.54%)
> Stddev 37 5409.49 ( 0.00%) 3192.12 ( 40.99%)
> Stddev 46 4521.95 ( 0.00%) 7392.52 (-63.48%)
> Max 1 32738.00 ( 0.00%) 32719.00 ( -0.06%)
> Max 10 136039.00 ( 0.00%) 148614.00 ( 9.24%)
> Max 19 130566.00 ( 0.00%) 127418.00 ( -2.41%)
> Max 28 115404.00 ( 0.00%) 111254.00 ( -3.60%)
> Max 37 112118.00 ( 0.00%) 111732.00 ( -0.34%)
> Max 46 108541.00 ( 0.00%) 116849.00 ( 7.65%)
> TPut 1 123813.00 ( 0.00%) 127671.00 ( 3.12%)
> TPut 10 497730.00 ( 0.00%) 563616.00 ( 13.24%)
> TPut 19 464134.00 ( 0.00%) 477179.00 ( 2.81%)
> TPut 28 433461.00 ( 0.00%) 427518.00 ( -1.37%)
> TPut 37 411939.00 ( 0.00%) 427697.00 ( 3.83%)
> TPut 46 403133.00 ( 0.00%) 421474.00 ( 4.55%)
>
> 3.17.0-rc2 3.17.0-rc2
> vanillanodeorder-v1r1
> DMA allocs 0 0
> DMA32 allocs 57 1491992
> Normal allocs 32543566 30026383
> Movable allocs 0 0
> Direct pages scanned 0 0
> Kswapd pages scanned 0 0
> Kswapd pages reclaimed 0 0
> Direct pages reclaimed 0 0
> Kswapd efficiency 100% 100%
> Kswapd velocity 0.000 0.000
> Direct efficiency 100% 100%
> Direct velocity 0.000 0.000
> Percentage direct scans 0% 0%
> Zone normal velocity 0.000 0.000
> Zone dma32 velocity 0.000 0.000
> Zone dma velocity 0.000 0.000
> THP fault alloc 55164 52987
> THP collapse alloc 139 147
> THP splits 26 21
> NUMA alloc hit 4169066 4250692
> NUMA alloc miss 0 0
>
> Note that there were more DMA32 allocations with the patch applied. In this
> particular case there was no difference in numa_hit and numa_miss. The
> expectation is that DMA32 was being used at the low watermark instead of
> falling into the slow path. kswapd was not woken but it's not worken for
> THP allocations.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
I agree. When I introduced the option(at ia64 numa development), there might be
some troubles. Recent NUMA tend to have enough memory on node0.
And problems can be avoided with numa_zonelist_order" "boot option, anyway.
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/page_alloc.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 18cee0d..20059aa 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3579,6 +3579,17 @@ static void build_zonelists_in_zone_order(pg_data_t *pgdat, int nr_nodes)
> zonelist->_zonerefs[pos].zone_idx = 0;
> }
>
> +#if defined(CONFIG_64BIT)
> +
> +/* Devices that require DMA32/DMA are relatively rare and do not justify a
> + * penalty to every machine in case the specialised case applies. Default
> + * to Node-ordering on 64-bit NUMA machines
> + */
> +static int default_zonelist_order(void)
> +{
> + return ZONELIST_ORDER_NODE;
> +}
> +#else
> static int default_zonelist_order(void)
> {
> int nid, zone_type;
> @@ -3641,6 +3652,7 @@ static int default_zonelist_order(void)
> }
> return ZONELIST_ORDER_ZONE;
> }
> +#endif /* CONFIG_64BIT */
>
> static void set_zonelist_order(void)
> {
>
> --
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