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

[Jungseung Lee]

Hi,

>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 at chromium.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

This patch really could save boot time. 
Is there any reason this patch is not merged to mainline kernel?

Best Regards,
Jungseung Lee