[PATCH] mm/compaction: Optimize pageblock_pfn_to_page() for contiguous zone

[Joonsoo Kim]

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
 include/linux/mmzone.h |  1 +
 mm/compaction.c        | 60 +++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e23a9e7..573f9a9 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -521,6 +521,7 @@ struct zone {
 #endif
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
+       int                     contiguous;
        /* Set to true when the PG_migrate_skip bits should be cleared */
        bool                    compact_blockskip_flush;
 #endif
diff --git a/mm/compaction.c b/mm/compaction.c
index de3e1e7..ff5fb04 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -88,7 +88,7 @@ static inline bool migrate_async_suitable(int migratetype)
  * the first and last page of a pageblock and avoid checking each individual
  * page in a pageblock.
  */
-static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
+static struct page *__pageblock_pfn_to_page(unsigned long start_pfn,
                                unsigned long end_pfn, struct zone *zone)
 {
        struct page *start_page;
@@ -114,6 +114,56 @@ static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
        return start_page;
 }
 
+static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,
+                               unsigned long end_pfn, struct zone *zone)
+{
+       if (zone->contiguous == 1)
+               return pfn_to_page(start_pfn);
+
+       return __pageblock_pfn_to_page(start_pfn, end_pfn, zone);
+}
+
+static void check_zone_contiguous(struct zone *zone)
+{
+       unsigned long block_start_pfn = zone->zone_start_pfn;
+       unsigned long block_end_pfn;
+       unsigned long pfn;
+
+       /* Already checked */
+       if (zone->contiguous)
+               return;
+
+       printk("%s: %s\n", __func__, zone->name);
+       block_end_pfn = ALIGN(block_start_pfn + 1, pageblock_nr_pages);
+       for (; block_start_pfn < zone_end_pfn(zone);
+               block_start_pfn = block_end_pfn,
+               block_end_pfn += pageblock_nr_pages) {
+
+               block_end_pfn = min(block_end_pfn, zone_end_pfn(zone));
+
+               if (!__pageblock_pfn_to_page(block_start_pfn,
+                                       block_end_pfn, zone)) {
+                       /* We have hole */
+                       zone->contiguous = -1;
+                       printk("%s: %s: uncontiguous\n", __func__, zone->name);
+                       return;
+               }
+
+               /* Check validity of pfn within pageblock */
+               for (pfn = block_start_pfn; pfn < block_end_pfn; pfn++) {
+                       if (!pfn_valid_within(pfn)) {
+                               zone->contiguous = -1;
+                               printk("%s: %s: uncontiguous\n", __func__, zone->name);
+                               return;
+                       }
+               }
+       }
+
+       /* We don't have hole */
+       zone->contiguous = 1;
+       printk("%s: %s: contiguous\n", __func__, zone->name);
+}
+
 #ifdef CONFIG_COMPACTION
 
 /* Do not skip compaction more than 64 times */
@@ -948,6 +998,12 @@ static void isolate_freepages(struct compact_control *cc)
        unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
        struct list_head *freelist = &cc->freepages;
 
+       /* Work-around */
+       if (zone->contiguous == 1 &&
+               cc->free_pfn == zone_end_pfn(zone) &&
+               cc->free_pfn == cc->free_pfn & ~(pageblock_nr_pages-1))
+               cc->free_pfn -= pageblock_nr_pages;
+
        /*
         * Initialise the free scanner. The starting point is where we last
         * successfully isolated from, zone-cached value, or the end of the
@@ -1356,6 +1412,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
                ;
        }
 
+       check_zone_contiguous(zone);
+
        /*
         * Clear pageblock skip if there were failures recently and compaction
         * is about to be retried after being deferred. kswapd does not do
-- 
1.9.1

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