sched/numa: Migrate pages to local nodes quicker early in the lifetime of a task

Automatic NUMA Balancing uses a multi-stage pass to decide whether a page
should migrate to a local node. This filter avoids excessive ping-ponging
if a page is shared or used by threads that migrate cross-node frequently.

Threads inherit both page tables and the preferred node ID from the
parent. This means that threads can trigger hinting faults earlier than
a new task which delays scanning for a number of seconds. As it can be
load balanced very early in its lifetime there can be an unnecessary delay
before it starts migrating thread-local data. This patch migrates private
pages faster early in the lifetime of a thread using the sequence counter
as an identifier of new tasks.

With this patch applied, STREAM performance is the same as 4.17 even though
processes are not spread cross-node prematurely. Other workloads showed
a mix of minor gains and losses. This is somewhat expected most workloads
are not very sensitive to the starting conditions of a process.

                         4.19.0-rc5             4.19.0-rc5                 4.17.0
                         numab-v1r1       fastmigrate-v1r1                vanilla
MB/sec copy     43298.52 (   0.00%)    47335.46 (   9.32%)    47219.24 (   9.06%)
MB/sec scale    30115.06 (   0.00%)    32568.12 (   8.15%)    32527.56 (   8.01%)
MB/sec add      32825.12 (   0.00%)    36078.94 (   9.91%)    35928.02 (   9.45%)
MB/sec triad    32549.52 (   0.00%)    35935.94 (  10.40%)    35969.88 (  10.51%)

Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Jirka Hladky <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Linux-MM <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

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