Re: [PATCH 2/2] mm: compaction: update the cc->nr_migratepages when allocating or freeing the freepages

[Mel Gorman]

On Mon, Jan 22, 2024 at 09:01:54PM +0800, Baolin Wang wrote:
> Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison
> to ensure that enough freepages are isolated in isolate_freepages(), however
> it just decreases the cc->nr_freepages without updating cc->nr_migratepages
> in compaction_alloc(), which will waste more CPU cycles and cause too many
> freepages to be isolated.
> 
> So we should also update the cc->nr_migratepages when allocating or freeing
> the freepages to avoid isolating excess freepages. And I can see fewer free
> pages are scanned and isolated when running thpcompact on my Arm64 server:
>                                        k6.7         k6.7_patched
> Ops Compaction pages isolated      120692036.00   118160797.00
> Ops Compaction migrate scanned     131210329.00   154093268.00
> Ops Compaction free scanned       1090587971.00  1080632536.00
> Ops Compact scan efficiency               12.03          14.26
> 
> Moreover, I did not see an obvious latency improvements, this is likely because
> isolating freepages is not the bottleneck in the thpcompact test case.
>                               k6.7                  k6.7_patched
> Amean     fault-both-1      1089.76 (   0.00%)     1080.16 *   0.88%*
> Amean     fault-both-3      1616.48 (   0.00%)     1636.65 *  -1.25%*
> Amean     fault-both-5      2266.66 (   0.00%)     2219.20 *   2.09%*
> Amean     fault-both-7      2909.84 (   0.00%)     2801.90 *   3.71%*
> Amean     fault-both-12     4861.26 (   0.00%)     4733.25 *   2.63%*
> Amean     fault-both-18     7351.11 (   0.00%)     6950.51 *   5.45%*
> Amean     fault-both-24     9059.30 (   0.00%)     9159.99 *  -1.11%*
> Amean     fault-both-30    10685.68 (   0.00%)    11399.02 *  -6.68%*
> 
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

-- 
Mel Gorman
SUSE Labs