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SubjectRe: [PATCH] mm: page_alloc: High-order per-cpu page allocator v3
On Mon, Nov 28, 2016 at 12:00:41PM +0100, Vlastimil Babka wrote:
> On 11/27/2016 02:19 PM, Mel Gorman wrote:
> >
> > 2-socket modern machine
> > 4.9.0-rc5 4.9.0-rc5
> > vanilla hopcpu-v3
> > Hmean send-64 178.38 ( 0.00%) 256.74 ( 43.93%)
> > Hmean send-128 351.49 ( 0.00%) 507.52 ( 44.39%)
> > Hmean send-256 671.23 ( 0.00%) 1004.19 ( 49.60%)
> > Hmean send-1024 2663.60 ( 0.00%) 3910.42 ( 46.81%)
> > Hmean send-2048 5126.53 ( 0.00%) 7562.13 ( 47.51%)
> > Hmean send-3312 7949.99 ( 0.00%) 11565.98 ( 45.48%)
> > Hmean send-4096 9433.56 ( 0.00%) 12929.67 ( 37.06%)
> > Hmean send-8192 15940.64 ( 0.00%) 21587.63 ( 35.43%)
> > Hmean send-16384 26699.54 ( 0.00%) 32013.79 ( 19.90%)
> > Hmean recv-64 178.38 ( 0.00%) 256.72 ( 43.92%)
> > Hmean recv-128 351.49 ( 0.00%) 507.47 ( 44.38%)
> > Hmean recv-256 671.20 ( 0.00%) 1003.95 ( 49.57%)
> > Hmean recv-1024 2663.45 ( 0.00%) 3909.70 ( 46.79%)
> > Hmean recv-2048 5126.26 ( 0.00%) 7560.67 ( 47.49%)
> > Hmean recv-3312 7949.50 ( 0.00%) 11564.63 ( 45.48%)
> > Hmean recv-4096 9433.04 ( 0.00%) 12927.48 ( 37.04%)
> > Hmean recv-8192 15939.64 ( 0.00%) 21584.59 ( 35.41%)
> > Hmean recv-16384 26698.44 ( 0.00%) 32009.77 ( 19.89%)
> >
> > 1-socket 6 year old machine
> > 4.9.0-rc5 4.9.0-rc5
> > vanilla hopcpu-v3
> > Hmean send-64 87.47 ( 0.00%) 127.14 ( 45.36%)
> > Hmean send-128 174.36 ( 0.00%) 256.42 ( 47.06%)
> > Hmean send-256 347.52 ( 0.00%) 509.41 ( 46.59%)
> > Hmean send-1024 1363.03 ( 0.00%) 1991.54 ( 46.11%)
> > Hmean send-2048 2632.68 ( 0.00%) 3759.51 ( 42.80%)
> > Hmean send-3312 4123.19 ( 0.00%) 5873.28 ( 42.45%)
> > Hmean send-4096 5056.48 ( 0.00%) 7072.81 ( 39.88%)
> > Hmean send-8192 8784.22 ( 0.00%) 12143.92 ( 38.25%)
> > Hmean send-16384 15081.60 ( 0.00%) 19812.71 ( 31.37%)
> > Hmean recv-64 86.19 ( 0.00%) 126.59 ( 46.87%)
> > Hmean recv-128 173.93 ( 0.00%) 255.21 ( 46.73%)
> > Hmean recv-256 346.19 ( 0.00%) 506.72 ( 46.37%)
> > Hmean recv-1024 1358.28 ( 0.00%) 1980.03 ( 45.77%)
> > Hmean recv-2048 2623.45 ( 0.00%) 3729.35 ( 42.15%)
> > Hmean recv-3312 4108.63 ( 0.00%) 5831.47 ( 41.93%)
> > Hmean recv-4096 5037.25 ( 0.00%) 7021.59 ( 39.39%)
> > Hmean recv-8192 8762.32 ( 0.00%) 12072.44 ( 37.78%)
> > Hmean recv-16384 15042.36 ( 0.00%) 19690.14 ( 30.90%)
>
> That looks way much better than the "v1" RFC posting. Was it just because
> you stopped doing the "at first iteration, use migratetype as index", and
> initializing pindex UINT_MAX hits so much quicker, or was there something
> more subtle that I missed? There was no changelog between "v1" and "v2".
>

The array is sized correctly which avoids one useless check. The order-0
lists are always drained first so in some rare cases, only the fast
paths are used. There was a subtle correction in detecting when all of
one list should be drained. In combination, it happened to boost
performance a lot on the two machines I reported on. While 6 other
machines were tested, not all of them saw such a dramatic boost and if
these machines are rebooted and retested every time, the high
performance is not always consistent, it all depends on how often the
fast paths are used.

> > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
>

Thanks.

--
Mel Gorman
SUSE Labs

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