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sched/numa: Skip some page migrations after a shared fault

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Shared faults can lead to lots of unnecessary page migrations,
slowing down the system, and causing private faults to hit the
per-pgdat migration ratelimit.

This patch adds sysctl numa_balancing_migrate_deferred, which specifies
how many shared page migrations to skip unconditionally, after each page
migration that is skipped because it is a shared fault.

This reduces the number of page migrations back and forth in
shared fault situations. It also gives a strong preference to
the tasks that are already running where most of the memory is,
and to moving the other tasks to near the memory.

Testing this with a much higher scan rate than the default
still seems to result in fewer page migrations than before.

Memory seems to be somewhat better consolidated than previously,
with multi-instance specjbb runs on a 4 node system.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-62-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Rik van Riel
2013-10-07 11:29:39 +01:00
committed by Ingo Molnar
parent 1e3646ffc6
commit de1c9ce6f0
5 changed files with 75 additions and 3 deletions
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10
Documentation/sysctl/kernel.txt
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@@ -375,7 +375,8 @@ feature should be disabled. Otherwise, if the system overhead from the
feature is too high then the rate the kernel samples for NUMA hinting
faults may be controlled by the numa_balancing_scan_period_min_ms,
numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
numa_balancing_scan_size_mb and numa_balancing_settle_count sysctls.
numa_balancing_scan_size_mb, numa_balancing_settle_count sysctls and
numa_balancing_migrate_deferred.
==============================================================
@@ -421,6 +422,13 @@ the schedule balancer stops pushing the task towards a preferred node. This
gives the scheduler a chance to place the task on an alternative node if the
preferred node is overloaded.
numa_balancing_migrate_deferred is how many page migrations get skipped
unconditionally, after a page migration is skipped because a page is shared
with other tasks. This reduces page migration overhead, and determines
how much stronger the "move task near its memory" policy scheduler becomes,
versus the "move memory near its task" memory management policy, for workloads
with shared memory.
==============================================================
osrelease, ostype & version: