mm, compaction: remove last_migrated_pfn from compact_control

The last_migrated_pfn field is a bit dubious as to whether it really
helps but either way, the information from it can be inferred without
increasing the size of compact_control so remove the field.

Link: http://lkml.kernel.org/r/20190118175136.31341-4-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>

2 files changed, 9 insertions, 17 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index c15b4bbc9e9e..e59dd7a7564c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -886,15 +886,6 @@ isolate_success:
                 cc->nr_migratepages++;
                 nr_isolated++;
 
-                /*
-                 * Record where we could have freed pages by migration and not
-                 * yet flushed them to buddy allocator.
-                 * - this is the lowest page that was isolated and likely be
-                 * then freed by migration.
-                 */
-                if (!cc->last_migrated_pfn)
-                        cc->last_migrated_pfn = low_pfn;
-
                 /* Avoid isolating too much */
                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
                         ++low_pfn;
@@ -918,7 +909,6 @@ isolate_fail:
                         }
                         putback_movable_pages(&cc->migratepages);
                         cc->nr_migratepages = 0;
-                        cc->last_migrated_pfn = 0;
                         nr_isolated = 0;
                 }
 
@@ -1539,6 +1529,7 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
         enum compact_result ret;
         unsigned long start_pfn = zone->zone_start_pfn;
         unsigned long end_pfn = zone_end_pfn(zone);
+        unsigned long last_migrated_pfn;
         const bool sync = cc->mode != MIGRATE_ASYNC;
 
         cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
@@ -1584,7 +1575,7 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
                         cc->whole_zone = true;
         }
 
-        cc->last_migrated_pfn = 0;
+        last_migrated_pfn = 0;
 
         trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
                                 cc->free_pfn, end_pfn, sync);
@@ -1593,12 +1584,14 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
 
         while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
                 int err;
+                unsigned long start_pfn = cc->migrate_pfn;
 
                 switch (isolate_migratepages(zone, cc)) {
                 case ISOLATE_ABORT:
                         ret = COMPACT_CONTENDED;
                         putback_movable_pages(&cc->migratepages);
                         cc->nr_migratepages = 0;
+                        last_migrated_pfn = 0;
                         goto out;
                 case ISOLATE_NONE:
                         /*
@@ -1608,6 +1601,7 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
                          */
                         goto check_drain;
                 case ISOLATE_SUCCESS:
+                        last_migrated_pfn = start_pfn;
                         ;
                 }
 
@@ -1639,8 +1633,7 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
                                 cc->migrate_pfn = block_end_pfn(
                                                 cc->migrate_pfn - 1, cc->order);
                                 /* Draining pcplists is useless in this case */
-                                cc->last_migrated_pfn = 0;
-
+                                last_migrated_pfn = 0;
                         }
                 }
 
@@ -1652,18 +1645,18 @@ check_drain:
                  * compact_finished() can detect immediately if allocation
                  * would succeed.
                  */
-                if (cc->order > 0 && cc->last_migrated_pfn) {
+                if (cc->order > 0 && last_migrated_pfn) {
                         int cpu;
                         unsigned long current_block_start =
                                 block_start_pfn(cc->migrate_pfn, cc->order);
 
-                        if (cc->last_migrated_pfn < current_block_start) {
+                        if (last_migrated_pfn < current_block_start) {
                                 cpu = get_cpu();
                                 lru_add_drain_cpu(cpu);
                                 drain_local_pages(zone);
                                 put_cpu();
                                 /* No more flushing until we migrate again */
-                                cc->last_migrated_pfn = 0;
+                                last_migrated_pfn = 0;
                         }
                 }
 
diff --git a/mm/internal.h b/mm/internal.h
index 867af5425432..f40d06d70683 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -188,7 +188,6 @@ struct compact_control {
         unsigned int nr_migratepages;   /* Number of pages to migrate */
         unsigned long free_pfn;         /* isolate_freepages search base */
         unsigned long migrate_pfn;      /* isolate_migratepages search base */
-        unsigned long last_migrated_pfn;/* Not yet flushed page being freed */
         struct zone *zone;
         unsigned long total_migrate_scanned;
         unsigned long total_free_scanned;