Re: [PATCH 10/19] mm: page_alloc: Reduce number of times page_to_pfn is called

Vlastimil Babka <vbabka@xxxxxxx> · Tue, 13 May 2014 15:27:29 +0200

On 05/13/2014 11:45 AM, Mel Gorman wrote:
In the free path we calculate page_to_pfn multiple times. Reduce that.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Just two comments.
I just don't like #define but I can live with that.
__free_one_page() is marked inline so presumably it would reuse 
page_to_pfn() result in its caller already. But it seems to me it's 
quite large so I wonder if it gets inlined anyway, and if the attribute 
still makes sense...

---
  include/linux/mmzone.h          |  9 +++++++--
  include/linux/pageblock-flags.h | 33 +++++++++++++--------------------
  mm/page_alloc.c                 | 34 +++++++++++++++++++---------------
  3 files changed, 39 insertions(+), 37 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 835aa3d..bd6f504 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -78,10 +78,15 @@ extern int page_group_by_mobility_disabled;
  #define NR_MIGRATETYPE_BITS (PB_migrate_end - PB_migrate + 1)
  #define MIGRATETYPE_MASK ((1UL << NR_MIGRATETYPE_BITS) - 1)

-static inline int get_pageblock_migratetype(struct page *page)
+#define get_pageblock_migratetype(page)					\
+	get_pfnblock_flags_mask(page, page_to_pfn(page),		\
+			PB_migrate_end, MIGRATETYPE_MASK)
+
+static inline int get_pfnblock_migratetype(struct page *page, unsigned long pfn)
  {
  	BUILD_BUG_ON(PB_migrate_end - PB_migrate != 2);
-	return get_pageblock_flags_mask(page, PB_migrate_end, MIGRATETYPE_MASK);
+	return get_pfnblock_flags_mask(page, pfn, PB_migrate_end,
+					MIGRATETYPE_MASK);
  }

  struct free_area {
diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index c08730c..2baeee1 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -65,33 +65,26 @@ extern int pageblock_order;
  /* Forward declaration */
  struct page;

-unsigned long get_pageblock_flags_mask(struct page *page,
+unsigned long get_pfnblock_flags_mask(struct page *page,
+				unsigned long pfn,
  				unsigned long end_bitidx,
  				unsigned long mask);
-void set_pageblock_flags_mask(struct page *page,
+
+void set_pfnblock_flags_mask(struct page *page,
  				unsigned long flags,
+				unsigned long pfn,
  				unsigned long end_bitidx,
  				unsigned long mask);

  /* Declarations for getting and setting flags. See mm/page_alloc.c */
-static inline unsigned long get_pageblock_flags_group(struct page *page,
-					int start_bitidx, int end_bitidx)
-{
-	unsigned long nr_flag_bits = end_bitidx - start_bitidx + 1;
-	unsigned long mask = (1 << nr_flag_bits) - 1;
-
-	return get_pageblock_flags_mask(page, end_bitidx, mask);
-}
-
-static inline void set_pageblock_flags_group(struct page *page,
-					unsigned long flags,
-					int start_bitidx, int end_bitidx)
-{
-	unsigned long nr_flag_bits = end_bitidx - start_bitidx + 1;
-	unsigned long mask = (1 << nr_flag_bits) - 1;
-
-	set_pageblock_flags_mask(page, flags, end_bitidx, mask);
-}
+#define get_pageblock_flags_group(page, start_bitidx, end_bitidx) \
+	get_pfnblock_flags_mask(page, page_to_pfn(page),		\
+			end_bitidx,					\
+			(1 << (end_bitidx - start_bitidx + 1)) - 1)
+#define set_pageblock_flags_group(page, flags, start_bitidx, end_bitidx) \
+	set_pfnblock_flags_mask(page, flags, page_to_pfn(page),		\
+			end_bitidx,					\
+			(1 << (end_bitidx - start_bitidx + 1)) - 1)

  #ifdef CONFIG_COMPACTION
  #define get_pageblock_skip(page) \
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b438eb7..3948f0a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -559,6 +559,7 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
   */

  static inline void __free_one_page(struct page *page,
+		unsigned long pfn,
  		struct zone *zone, unsigned int order,
  		int migratetype)
  {
@@ -575,7 +576,7 @@ static inline void __free_one_page(struct page *page,

  	VM_BUG_ON(migratetype == -1);

-	page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
+	page_idx = pfn & ((1 << MAX_ORDER) - 1);

  	VM_BUG_ON_PAGE(page_idx & ((1 << order) - 1), page);
  	VM_BUG_ON_PAGE(bad_range(zone, page), page);
@@ -710,7 +711,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
  			list_del(&page->lru);
  			mt = get_freepage_migratetype(page);
  			/* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
-			__free_one_page(page, zone, 0, mt);
+			__free_one_page(page, page_to_pfn(page), zone, 0, mt);
  			trace_mm_page_pcpu_drain(page, 0, mt);
  			if (likely(!is_migrate_isolate_page(page))) {
  				__mod_zone_page_state(zone, NR_FREE_PAGES, 1);
@@ -722,13 +723,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
  	spin_unlock(&zone->lock);
  }

-static void free_one_page(struct zone *zone, struct page *page, int order,
+static void free_one_page(struct zone *zone,
+				struct page *page, unsigned long pfn,
+				int order,
  				int migratetype)
  {
  	spin_lock(&zone->lock);
  	zone->pages_scanned = 0;

-	__free_one_page(page, zone, order, migratetype);
+	__free_one_page(page, pfn, zone, order, migratetype);
  	if (unlikely(!is_migrate_isolate(migratetype)))
  		__mod_zone_freepage_state(zone, 1 << order, migratetype);
  	spin_unlock(&zone->lock);
@@ -765,15 +768,16 @@ static void __free_pages_ok(struct page *page, unsigned int order)
  {
  	unsigned long flags;
  	int migratetype;
+	unsigned long pfn = page_to_pfn(page);

  	if (!free_pages_prepare(page, order))
  		return;

  	local_irq_save(flags);
  	__count_vm_events(PGFREE, 1 << order);
-	migratetype = get_pageblock_migratetype(page);
+	migratetype = get_pfnblock_migratetype(page, pfn);
  	set_freepage_migratetype(page, migratetype);
-	free_one_page(page_zone(page), page, order, migratetype);
+	free_one_page(page_zone(page), page, pfn, order, migratetype);
  	local_irq_restore(flags);
  }

@@ -1376,12 +1380,13 @@ void free_hot_cold_page(struct page *page, int cold)
  	struct zone *zone = page_zone(page);
  	struct per_cpu_pages *pcp;
  	unsigned long flags;
+	unsigned long pfn = page_to_pfn(page);
  	int migratetype;

  	if (!free_pages_prepare(page, 0))
  		return;

-	migratetype = get_pageblock_migratetype(page);
+	migratetype = get_pfnblock_migratetype(page, pfn);
  	set_freepage_migratetype(page, migratetype);
  	local_irq_save(flags);
  	__count_vm_event(PGFREE);
@@ -1395,7 +1400,7 @@ void free_hot_cold_page(struct page *page, int cold)
  	 */
  	if (migratetype >= MIGRATE_PCPTYPES) {
  		if (unlikely(is_migrate_isolate(migratetype))) {
-			free_one_page(zone, page, 0, migratetype);
+			free_one_page(zone, page, pfn, 0, migratetype);
  			goto out;
  		}
  		migratetype = MIGRATE_MOVABLE;
@@ -6032,17 +6037,16 @@ static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
   * @end_bitidx: The last bit of interest
   * returns pageblock_bits flags
   */
-unsigned long get_pageblock_flags_mask(struct page *page,
+unsigned long get_pfnblock_flags_mask(struct page *page, unsigned long pfn,
  					unsigned long end_bitidx,
  					unsigned long mask)
  {
  	struct zone *zone;
  	unsigned long *bitmap;
-	unsigned long pfn, bitidx, word_bitidx;
+	unsigned long bitidx, word_bitidx;
  	unsigned long word;

  	zone = page_zone(page);
-	pfn = page_to_pfn(page);
  	bitmap = get_pageblock_bitmap(zone, pfn);
  	bitidx = pfn_to_bitidx(zone, pfn);
  	word_bitidx = bitidx / BITS_PER_LONG;
@@ -6054,25 +6058,25 @@ unsigned long get_pageblock_flags_mask(struct page *page,
  }

  /**
- * set_pageblock_flags_mask - Set the requested group of flags for a pageblock_nr_pages block of pages
+ * set_pfnblock_flags_mask - Set the requested group of flags for a pageblock_nr_pages block of pages
   * @page: The page within the block of interest
   * @start_bitidx: The first bit of interest
   * @end_bitidx: The last bit of interest
   * @flags: The flags to set
   */
-void set_pageblock_flags_mask(struct page *page, unsigned long flags,
+void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
+					unsigned long pfn,
  					unsigned long end_bitidx,
  					unsigned long mask)
  {
  	struct zone *zone;
  	unsigned long *bitmap;
-	unsigned long pfn, bitidx, word_bitidx;
+	unsigned long bitidx, word_bitidx;
  	unsigned long old_word, word;

  	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);

  	zone = page_zone(page);
-	pfn = page_to_pfn(page);
  	bitmap = get_pageblock_bitmap(zone, pfn);
  	bitidx = pfn_to_bitidx(zone, pfn);
  	word_bitidx = bitidx / BITS_PER_LONG;


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