Fix: mm_compaction_migratepages changed in linux 6.9-rc1
authorKienan Stewart <kstewart@efficios.com>
Mon, 25 Mar 2024 14:30:32 +0000 (10:30 -0400)
committerMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Wed, 27 Mar 2024 13:27:26 +0000 (09:27 -0400)
commitf4a6415f8d5fa447868d1fdc7119e0a328966379
tree3413f48b99d4d1039e0383736054091015cf941a
parentd8379ec6365a925db33cae94fb6783cdbdb6a922
Fix: mm_compaction_migratepages changed in linux 6.9-rc1

See upstream commit:

    commit ab755bf4249b992fc2140d615ab0a686d50765b4
    Author: Baolin Wang <baolin.wang@linux.alibaba.com>
    Date:   Tue Feb 20 14:16:31 2024 +0800

        mm: compaction: update the cc->nr_migratepages when allocating or freeing the freepages

        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%*

Change-Id: I103a43fd1b549360b3fc978fd409b7c17ef3e192
Signed-off-by: Kienan Stewart <kstewart@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
include/instrumentation/events/compaction.h
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