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%)

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Mel Gorman <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: YueHaibing <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/compaction.c b/mm/compaction.c
index 68e3c214bcbdfad1c41d6345f2c508b93da70846..9c7d43fd465567dd29e992712df14551f0e641a4 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -404,21 +404,6 @@ static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
        return true;
 }
 
-/*
- * Aside from avoiding lock contention, compaction also periodically checks
- * need_resched() and records async compaction as contended if necessary.
- */
-static inline void compact_check_resched(struct compact_control *cc)
-{
-       /* async compaction aborts if contended */
-       if (need_resched()) {
-               if (cc->mode == MIGRATE_ASYNC)
-                       cc->contended = true;
-
-               cond_resched();
-       }
-}
-
 /*
  * Compaction requires the taking of some coarse locks that are potentially
  * very heavily contended. The lock should be periodically unlocked to avoid
@@ -447,7 +432,7 @@ static bool compact_unlock_should_abort(spinlock_t *lock,
                return true;
        }
 
-       compact_check_resched(cc);
+       cond_resched();
 
        return false;
 }
@@ -736,7 +721,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
                        return 0;
        }
 
-       compact_check_resched(cc);
+       cond_resched();
 
        if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
                skip_on_failure = true;
@@ -1370,7 +1355,7 @@ static void isolate_freepages(struct compact_control *cc)
                 * suitable migration targets, so periodically check resched.
                 */
                if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
-                       compact_check_resched(cc);
+                       cond_resched();
 
                page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
                                                                        zone);
@@ -1666,7 +1651,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
                 * need to schedule.
                 */
                if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
-                       compact_check_resched(cc);
+                       cond_resched();
 
                page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
                                                                        zone);