On Mon, Dec 28, 2015 at 2:15 AM, Jungseung Lee [off-list ref] wrote:

Hi,

quoted

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 <redacted>
---
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)

quoted

#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);

quoted

#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);

quoted

/*
 * 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?

Well it was ignored when I originally posted it so I assumed mainline
developers weren't really interested.  I can re-spin and send a new
version if there's interest in getting it merged now.

Best Regards,
Jungseung Lee