• Mel Gorman's avatar
    sched/numa: Set the scan rate proportional to the memory usage of the task being scanned · 598f0ec0
    Mel Gorman authored
    The NUMA PTE scan rate is controlled with a combination of the
    numa_balancing_scan_period_min, numa_balancing_scan_period_max and
    numa_balancing_scan_size. This scan rate is independent of the size
    of the task and as an aside it is further complicated by the fact that
    numa_balancing_scan_size controls how many pages are marked pte_numa and
    not how much virtual memory is scanned.
    
    In combination, it is almost impossible to meaningfully tune the min and
    max scan periods and reasoning about performance is complex when the time
    to complete a full scan is is partially a function of the tasks memory
    size. This patch alters the semantic of the min and max tunables to be
    about tuning the length time it takes to complete a scan of a tasks occupied
    virtual address space. Conceptually this is a lot easier to understand. There
    is a "sanity" check to ensure the scan rate is never extremely fast based on
    the amount of virtual memory that should be scanned in a second. The default
    of 2.5G seems arbitrary but it is to have the maximum scan rate after the
    patch roughly match the maximum scan rate before the patch was applied.
    
    On a similar note, numa_scan_period is in milliseconds and not
    jiffies. Properly placed pages slow the scanning rate but adding 10 jiffies
    to numa_scan_period means that the rate scanning slows depends on HZ which
    is confusing. Get rid of the jiffies_to_msec conversion and treat it as ms.
    Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
    Reviewed-by: default avatarRik van Riel <riel@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1381141781-10992-18-git-send-email-mgorman@suse.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    598f0ec0
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