• Mel Gorman's avatar
    mm, sched/numa: Remove rate-limiting of automatic NUMA balancing migration · efaffc5e
    Mel Gorman authored
    Rate limiting of page migrations due to automatic NUMA balancing was
    introduced to mitigate the worst-case scenario of migrating at high
    frequency due to false sharing or slowly ping-ponging between nodes.
    Since then, a lot of effort was spent on correctly identifying these
    pages and avoiding unnecessary migrations and the safety net may no longer
    be required.
    
    Jirka Hladky reported a regression in 4.17 due to a scheduler patch that
    avoids spreading STREAM tasks wide prematurely. However, once the task
    was properly placed, it delayed migrating the memory due to rate limiting.
    Increasing the limit fixed the problem for him.
    
    Currently, the limit is hard-coded and does not account for the real
    capabilities of the hardware. Even if an estimate was attempted, it would
    not properly account for the number of memory controllers and it could
    not account for the amount of bandwidth used for normal accesses. Rather
    than fudging, this patch simply eliminates the rate limiting.
    
    However, Jirka reports that a STREAM configuration using multiple
    processes achieved similar performance to 4.16. In local tests, this patch
    improved performance of STREAM relative to the baseline but it is somewhat
    machine-dependent. Most workloads show little or not performance difference
    implying that there is not a heavily reliance on the throttling mechanism
    and it is safe to remove.
    
    STREAM on 2-socket machine
                             4.19.0-rc5             4.19.0-rc5
                             numab-v1r1       noratelimit-v1r1
    MB/sec copy     43298.52 (   0.00%)    44673.38 (   3.18%)
    MB/sec scale    30115.06 (   0.00%)    31293.06 (   3.91%)
    MB/sec add      32825.12 (   0.00%)    34883.62 (   6.27%)
    MB/sec triad    32549.52 (   0.00%)    34906.60 (   7.24%
    Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
    Reviewed-by: default avatarRik van Riel <riel@surriel.com>
    Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Jirka Hladky <jhladky@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Linux-MM <linux-mm@kvack.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20181001100525.29789-2-mgorman@techsingularity.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    efaffc5e
migrate.c 75.8 KB