Re: Suspicious error for CMA stress test

Joonsoo Kim
2016-03-14T07:17:17Z

On Mon, Mar 14, 2016 at 08:06:16AM +0100, Vlastimil Babka wrote:
> On 03/14/2016 07:49 AM, Joonsoo Kim wrote:
> >On Fri, Mar 11, 2016 at 06:07:40PM +0100, Vlastimil Babka wrote:
> >>On 03/11/2016 04:00 PM, Joonsoo Kim wrote:
> >>
> >>How about something like this? Just and idea, probably buggy (off-by-one etc.).
> >>Should keep away cost from <pageblock_order iterations at the expense of the
> >>relatively fewer >pageblock_order iterations.
> >
> >Hmm... I tested this and found that it's code size is a little bit
> >larger than mine. I'm not sure why this happens exactly but I guess it would be
> >related to compiler optimization. In this case, I'm in favor of my
> >implementation because it looks like well abstraction. It adds one
> >unlikely branch to the merge loop but compiler would optimize it to
> >check it once.
>
> I would be surprised if compiler optimized that to check it once, as
> order increases with each loop iteration. But maybe it's smart
> enough to do something like I did by hand? Guess I'll check the
> disassembly.

Okay. I used following slightly optimized version and I need to
add 'max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1)'
to yours. Please consider it, too.

Thanks.

------------------------>8------------------------
>From 36b8ffdaa0e7a8d33fd47a62a35a9e507e3e62e9 Mon Sep 17 00:00:00 2001
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Date: Mon, 14 Mar 2016 15:20:07 +0900
Subject: [PATCH] mm: fix cma

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
---
mm/page_alloc.c | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0bb933a..f7baa4f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -627,8 +627,8 @@ static inline void rmv_page_order(struct page *page)
*
* For recording page's order, we use page_private(page).
*/
-static inline int page_is_buddy(struct page *page, struct page *buddy,
- unsigned int order)
+static inline int page_is_buddy(struct zone *zone, struct page *page,
+ struct page *buddy, unsigned int order, int mt)
{
if (!pfn_valid_within(page_to_pfn(buddy)))
return 0;
@@ -651,6 +651,15 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
if (page_zone_id(page) != page_zone_id(buddy))
return 0;

+ if (unlikely(has_isolate_pageblock(zone) &&
+ order >= pageblock_order)) {
+ int buddy_mt = get_pageblock_migratetype(buddy);
+
+ if (mt != buddy_mt && (is_migrate_isolate(mt) ||
+ is_migrate_isolate(buddy_mt)))
+ return 0;
+ }
+
VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);

return 1;
@@ -698,17 +707,8 @@ static inline void __free_one_page(struct page *page,
VM_BUG_ON_PAGE(page->flags & PAGE_FLAGS_CHECK_AT_PREP, page);

VM_BUG_ON(migratetype == -1);
- if (is_migrate_isolate(migratetype)) {
- /*
- * We restrict max order of merging to prevent merge
- * between freepages on isolate pageblock and normal
- * pageblock. Without this, pageblock isolation
- * could cause incorrect freepage accounting.
- */
- max_order = min_t(unsigned int, MAX_ORDER, pageblock_order + 1);
- } else {
+ if (!is_migrate_isolate(migratetype))
__mod_zone_freepage_state(zone, 1 << order, migratetype);
- }

page_idx = pfn & ((1 << max_order) - 1);

@@ -718,7 +718,7 @@ static inline void __free_one_page(struct page *page,
while (order < max_order - 1) {
buddy_idx = __find_buddy_index(page_idx, order);
buddy = page + (buddy_idx - page_idx);
- if (!page_is_buddy(page, buddy, order))
+ if (!page_is_buddy(zone, page, buddy, order, migratetype))
break;
/*
* Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
@@ -752,7 +752,8 @@ static inline void __free_one_page(struct page *page,
higher_page = page + (combined_idx - page_idx);
buddy_idx = __find_buddy_index(combined_idx, order + 1);
higher_buddy = higher_page + (buddy_idx - combined_idx);
- if (page_is_buddy(higher_page, higher_buddy, order + 1)) {
+ if (page_is_buddy(zone, higher_page, higher_buddy,
+ order + 1, migratetype)) {
list_add_tail(&page->lru,
&zone->free_area[order].free_list[migratetype]);
goto out;
--
1.9.1