[patch -mm 3/3] mm, compaction: avoid compacting memory for thp if pageblock cannot become free

David Rientjes
2014-06-04T00:30:11Z

It's pointless to migrate pages within a pageblock if the entire pageblock will
not become free for a thp allocation.

If we encounter a page that cannot be migrated and a direct compactor other than
khugepaged is trying to allocate a hugepage for thp, then skip the entire
pageblock and avoid migrating pages needlessly.

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/compaction.c | 41 ++++++++++++++++++++++++++++-------------
1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -537,12 +537,12 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
if (!pfn_valid(low_pfn)) {
low_pfn += MAX_ORDER_NR_PAGES - 1;
- continue;
+ goto next;
}
}

if (!pfn_valid_within(low_pfn))
- continue;
+ goto next;
nr_scanned++;

/*
@@ -553,7 +553,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
*/
page = pfn_to_page(low_pfn);
if (page_zone(page) != zone)
- continue;
+ goto next;

if (!valid_page)
valid_page = page;
@@ -599,7 +599,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
goto isolate_success;
}
}
- continue;
+ goto next;
}

/*
@@ -616,7 +616,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
if (!locked)
goto next_pageblock;
low_pfn += (1 << compound_order(page)) - 1;
- continue;
+ goto next;
}

/*
@@ -626,7 +626,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
*/
if (!page_mapping(page) &&
page_count(page) > page_mapcount(page))
- continue;
+ goto next;

/* Check if it is ok to still hold the lock */
locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
@@ -636,17 +636,17 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,

/* Recheck PageLRU and PageTransHuge under lock */
if (!PageLRU(page))
- continue;
+ goto next;
if (PageTransHuge(page)) {
low_pfn += (1 << compound_order(page)) - 1;
- continue;
+ goto next;
}

lruvec = mem_cgroup_page_lruvec(page, zone);

/* Try isolate the page */
if (__isolate_lru_page(page, mode) != 0)
- continue;
+ goto next;

VM_BUG_ON_PAGE(PageTransCompound(page), page);

@@ -669,6 +669,24 @@ isolate_success:

next_pageblock:
low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
+
+next:
+ /*
+ * It is too expensive for compaction to migrate pages from a
+ * pageblock for thp page faults unless the entire pageblock
+ * will become free.
+ */
+ if ((cc->gfp_mask & __GFP_NO_KSWAPD) &&
+ !(current->flags & PF_KTHREAD)) {
+ if (locked) {
+ spin_unlock_irqrestore(&zone->lru_lock, flags);
+ locked = false;
+ }
+ putback_movable_pages(migratelist);
+ cc->nr_migratepages = 0;
+ nr_isolated = 0;
+ low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
+ }
}

acct_isolated(zone, locked, cc);
@@ -880,7 +898,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,

cc->migrate_pfn = low_pfn;

- return ISOLATE_SUCCESS;
+ return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
}

static int compact_finished(struct zone *zone, struct compact_control *cc,
@@ -1055,9 +1073,6 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
;
}

- if (!cc->nr_migratepages)
- continue;
-
err = migrate_pages(&cc->migratepages, compaction_alloc,
compaction_free, (unsigned long)cc, cc->mode,
MR_COMPACTION);