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SubjectRe: [PATCH 5/6] Have ia64 use add_active_range() and free_area_init_nodes
On Tue, 16 May 2006 10:31:56 +1000
Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> >But clean-up/speed-up codes vanished these checks. (I don't know when this occurs)
> >Sorry for misses these things.
> >
>
> I think if anything they should be moved into page_is_buddy, however
> page_to_pfn
> is expensive on some architectures, so it is something we want to be
> able to opt
> out of if we do the correct alignment.
>

yes. It's expensive.
I received following e-Mail from Dave Hansen in past.
==
There are some ppc64 machines which have memory laid out like this:

0-100 MB Node0
100-200 MB Node1
200-300 MB Node0
==
I didn't imagine above (strange) configration.
So, simple range check will not work for all configration anyway.
(above example is aligned and has no problem. Moreover, ppc uses SPARSEMEM.)

Andy's page_zone(page) == page_zone(buddy) check is good, I think.

Making alignment is a difficult problem, I think. It complecates many things.
We can avoid above check only when memory layout is ideal.

BTW, How about following patch ?
I don't want to say "Oh, you have to re-compile your kernel with
CONFIG_UNALIGNED_ZONE on your new machine. you are unlucky." to users.

==

Index: linux-2.6.17-rc4-mm1/mm/page_alloc.c
===================================================================
--- linux-2.6.17-rc4-mm1.orig/mm/page_alloc.c
+++ linux-2.6.17-rc4-mm1/mm/page_alloc.c
@@ -58,6 +58,7 @@ unsigned long totalhigh_pages __read_mos
unsigned long totalreserve_pages __read_mostly;
long nr_swap_pages;
int percpu_pagelist_fraction;
+int unaligned_zone;

static void __free_pages_ok(struct page *page, unsigned int order);

@@ -296,12 +297,12 @@ static inline void rmv_page_order(struct
*
* Assumption: *_mem_map is contigious at least up to MAX_ORDER
*/
-static inline struct page *
+static inline long *
__page_find_buddy(struct page *page, unsigned long page_idx, unsigned int order)
{
unsigned long buddy_idx = page_idx ^ (1 << order);

- return page + (buddy_idx - page_idx);
+ return (buddy_idx - page_idx);
}

static inline unsigned long
@@ -310,6 +311,23 @@ __find_combined_index(unsigned long page
return (page_idx & ~(1 << order));
}

+static inline struct page *
+buddy_in_range(struct zone *zone, struct page *page, long buddy_idx)
+{
+ unsigned long pfn;
+ struct page *buddy;
+ if (!unaligned_zone)
+ return page + buddy_idx;
+ pfn = page_to_pfn(page);
+ if (!pfn_valid(pfn + buddy_idx))
+ return NULL;
+ buddy = page + buddy_idx;
+ if (page_zone_id(page) != page_zone_id(buddy))
+ return NULL;
+ return buddy;
+}
+
+
/*
* This function checks whether a page is free && is the buddy
* we can do coalesce a page and its buddy if
@@ -326,15 +344,10 @@ __find_combined_index(unsigned long page
static inline int page_is_buddy(struct page *page, struct page *buddy,
int order)
{
-#ifdef CONFIG_HOLES_IN_ZONE
+#if defined(CONFIG_HOLES_IN_ZONE)
if (!pfn_valid(page_to_pfn(buddy)))
return 0;
#endif
-#ifdef CONFIG_UNALIGNED_ZONE_BOUNDRIES
- if (page_zone_id(page) != page_zone_id(buddy))
- return 0;
-#endif
-
if (PageBuddy(buddy) && page_order(buddy) == order) {
BUG_ON(page_count(buddy) != 0);
return 1;
@@ -383,10 +396,14 @@ static inline void __free_one_page(struc
zone->free_pages += order_size;
while (order < MAX_ORDER-1) {
unsigned long combined_idx;
+ long buddy_idx;
struct free_area *area;
struct page *buddy;

- buddy = __page_find_buddy(page, page_idx, order);
+ buddy_idx = __page_find_buddy(page, page_idx, order);
+ buddy = buddy_in_zone(zone, page, buddy_idx);
+ if (unlikely(!buddy))
+ break;
if (!page_is_buddy(page, buddy, order))
break; /* Move the buddy up one level. */

@@ -2434,10 +2451,9 @@ static void __meminit free_area_init_cor
struct zone *zone = pgdat->node_zones + j;
unsigned long size, realsize;

- if (zone_boundary_align_pfn(zone_start_pfn) != zone_start_pfn)
- printk(KERN_CRIT "node %d zone %s missaligned "
- "start pfn, enable UNALIGNED_ZONE_BOUNDRIES\n",
- nid, zone_names[j]);
+ if (zone_boundary_align_pfn(zone_start_pfn) != zone_start_pfn) {
+ unaligned_zone = 1;
+ }

size = zone_present_pages_in_node(nid, j, zones_size);
realsize = size - zone_absent_pages_in_node(nid, j,
Index: linux-2.6.17-rc4-mm1/include/linux/mmzone.h
===================================================================
--- linux-2.6.17-rc4-mm1.orig/include/linux/mmzone.h
+++ linux-2.6.17-rc4-mm1/include/linux/mmzone.h
@@ -399,11 +399,7 @@ static inline int is_dma(struct zone *zo

static inline unsigned long zone_boundary_align_pfn(unsigned long pfn)
{
-#ifdef CONFIG_UNALIGNED_ZONE_BOUNDRIES
- return pfn;
-#else
return pfn & ~((1 << MAX_ORDER) - 1);
-#endif
}

/* These two functions are used to setup the per zone pages min values */


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