linux-kernel - [PATCH] ARM: mm: Speed up page list initialization during boot

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Date:	Fri, 21 Mar 2014 12:15:17 -0700
From:	Chirantan Ekbote <chirantan@...omium.org>
To:	linux@....linux.org.uk
Cc:	linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, sonnyrao@...omium.org,
	dianders@...omium.org, Chirantan Ekbote <chirantan@...omium.org>
Subject: [PATCH] ARM: mm: Speed up page list initialization during boot

During boot, we populate the page lists by using the page freeing
mechanism on every individual page.  Unfortunately, this is very
inefficient because the memory manager spends a lot of time coalescing
pairs of adjacent free pages into bigger blocks.

Rather than adding a single order 0 page at a time, we can take
advantage of the fact that we know that all the pages are available and
free up big blocks of pages at a time instead.

Signed-off-by: Chirantan Ekbote <chirantan@...omium.org>
---
 arch/arm/mm/init.c  | 19 +++++++++++++++++--
 include/linux/gfp.h |  1 +
 mm/internal.h       |  1 -
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 97c293e..c7fc2d8 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -22,6 +22,7 @@
 #include <linux/memblock.h>
 #include <linux/dma-contiguous.h>
 #include <linux/sizes.h>
+#include <linux/bitops.h>
 
 #include <asm/mach-types.h>
 #include <asm/memblock.h>
@@ -469,8 +470,22 @@ static void __init free_unused_memmap(struct meminfo *mi)
 #ifdef CONFIG_HIGHMEM
 static inline void free_area_high(unsigned long pfn, unsigned long end)
 {
-	for (; pfn < end; pfn++)
-		free_highmem_page(pfn_to_page(pfn));
+	while (pfn < end) {
+		struct page *page = pfn_to_page(pfn);
+		unsigned long order = min(__ffs(pfn), MAX_ORDER - 1);
+		unsigned long nr_pages = 1 << order;
+		unsigned long rem = end - pfn;
+
+		if (nr_pages > rem) {
+			order = __fls(rem);
+			nr_pages = 1 << order;
+		}
+
+		__free_pages_bootmem(page, order);
+		totalram_pages += nr_pages;
+		totalhigh_pages += nr_pages;
+		pfn += nr_pages;
+	}
 }
 #endif
 
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 39b81dc..a63d666 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -367,6 +367,7 @@ void *alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask);
 #define __get_dma_pages(gfp_mask, order) \
 		__get_free_pages((gfp_mask) | GFP_DMA, (order))
 
+extern void __free_pages_bootmem(struct page *page, unsigned int order);
 extern void __free_pages(struct page *page, unsigned int order);
 extern void free_pages(unsigned long addr, unsigned int order);
 extern void free_hot_cold_page(struct page *page, int cold);
diff --git a/mm/internal.h b/mm/internal.h
index 29e1e76..d2b8738 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -93,7 +93,6 @@ extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
 /*
  * in mm/page_alloc.c
  */
-extern void __free_pages_bootmem(struct page *page, unsigned int order);
 extern void prep_compound_page(struct page *page, unsigned long order);
 #ifdef CONFIG_MEMORY_FAILURE
 extern bool is_free_buddy_page(struct page *page);
-- 
1.9.1.423.g4596e3a

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