mm, compaction: do not consider a need to reschedule as contention

Scanning on large machines can take a considerable length of time and
eventually need to be rescheduled.  This is treated as an abort event
but that's not appropriate as the attempt is likely to be retried after
making numerous checks and taking another cycle through the page
allocator.  This patch will check the need to reschedule if necessary
but continue the scanning.

The main benefit is reduced scanning when compaction is taking a long
time or the machine is over-saturated.  It also avoids an unnecessary
exit of compaction that ends up being retried by the page allocator in
the outer loop.

                                     5.0.0-rc1              5.0.0-rc1
                              synccached-v3r16        noresched-v3r17
Amean     fault-both-1         0.00 (   0.00%)        0.00 *   0.00%*
Amean     fault-both-3      2958.27 (   0.00%)     2965.68 (  -0.25%)
Amean     fault-both-5      4091.90 (   0.00%)     3995.90 (   2.35%)
Amean     fault-both-7      5803.05 (   0.00%)     5842.12 (  -0.67%)
Amean     fault-both-12     9481.06 (   0.00%)     9550.87 (  -0.74%)
Amean     fault-both-18    14141.51 (   0.00%)    13304.72 (   5.92%)
Amean     fault-both-24    16438.00 (   0.00%)    14618.59 (  11.07%)
Amean     fault-both-30    17531.72 (   0.00%)    16650.96 (   5.02%)
Amean     fault-both-32    17101.96 (   0.00%)    17145.15 (  -0.25%)

Change-Id: I002a0fb5cfa1898e4a1ea5aa7c2111a4c9ced1a3
Link: http://lkml.kernel.org/r/20190118175136.31341-18-mgorman@techsingularity.net


Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: cf66f0700c8f1d7c7c1c1d7e5e846a1836814601
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>