linux-kernel - [PATCH 07/22] mm, page_alloc: Avoid unnecessary zone lookups during pageblock operations

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Message-Id: <1460362424-26369-8-git-send-email-mgorman@techsingularity.net>
Date:	Mon, 11 Apr 2016 09:13:30 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 07/22] mm, page_alloc: Avoid unnecessary zone lookups during pageblock operations

Pageblocks have an associated bitmap to store migrate types and whether
the pageblock should be skipped during compaction. The bitmap may be
associated with a memory section or a zone but the zone is looked up
unconditionally. The compiler should optimise this away automatically so
this is a cosmetic patch only in many cases.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ab16560b76e6..d00847bb1612 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6759,23 +6759,23 @@ void *__init alloc_large_system_hash(const char *tablename,
 }
 
 /* Return a pointer to the bitmap storing bits affecting a block of pages */
-static inline unsigned long *get_pageblock_bitmap(struct zone *zone,
+static inline unsigned long *get_pageblock_bitmap(struct page *page,
 							unsigned long pfn)
 {
 #ifdef CONFIG_SPARSEMEM
 	return __pfn_to_section(pfn)->pageblock_flags;
 #else
-	return zone->pageblock_flags;
+	return page_zone(page)->pageblock_flags;
 #endif /* CONFIG_SPARSEMEM */
 }
 
-static inline int pfn_to_bitidx(struct zone *zone, unsigned long pfn)
+static inline int pfn_to_bitidx(struct page *page, unsigned long pfn)
 {
 #ifdef CONFIG_SPARSEMEM
 	pfn &= (PAGES_PER_SECTION-1);
 	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
 #else
-	pfn = pfn - round_down(zone->zone_start_pfn, pageblock_nr_pages);
+	pfn = pfn - round_down(page_zone(page)->zone_start_pfn, pageblock_nr_pages);
 	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
 #endif /* CONFIG_SPARSEMEM */
 }
@@ -6793,14 +6793,12 @@ 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 bitidx, word_bitidx;
 	unsigned long word;
 
-	zone = page_zone(page);
-	bitmap = get_pageblock_bitmap(zone, pfn);
-	bitidx = pfn_to_bitidx(zone, pfn);
+	bitmap = get_pageblock_bitmap(page, pfn);
+	bitidx = pfn_to_bitidx(page, pfn);
 	word_bitidx = bitidx / BITS_PER_LONG;
 	bitidx &= (BITS_PER_LONG-1);
 
@@ -6822,20 +6820,18 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
 					unsigned long end_bitidx,
 					unsigned long mask)
 {
-	struct zone *zone;
 	unsigned long *bitmap;
 	unsigned long bitidx, word_bitidx;
 	unsigned long old_word, word;
 
 	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
 
-	zone = page_zone(page);
-	bitmap = get_pageblock_bitmap(zone, pfn);
-	bitidx = pfn_to_bitidx(zone, pfn);
+	bitmap = get_pageblock_bitmap(page, pfn);
+	bitidx = pfn_to_bitidx(page, pfn);
 	word_bitidx = bitidx / BITS_PER_LONG;
 	bitidx &= (BITS_PER_LONG-1);
 
-	VM_BUG_ON_PAGE(!zone_spans_pfn(zone, pfn), page);
+	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
 
 	bitidx += end_bitidx;
 	mask <<= (BITS_PER_LONG - bitidx - 1);
-- 
2.6.4