Re: Suspicious error for CMA stress test

Vlastimil Babka
2016-03-07T12:59:24Z

On 03/07/2016 05:34 AM, Joonsoo Kim wrote:
> On Fri, Mar 04, 2016 at 03:35:26PM +0800, Hanjun Guo wrote:
>>> Sad to hear that.
>>>
>>> Could you tell me your system's MAX_ORDER and pageblock_order?
>>>
>>
>> MAX_ORDER is 11, pageblock_order is 9, thanks for your help!

I thought that CMA regions/operations (and isolation IIRC?) were
supposed to be MAX_ORDER aligned exactly to prevent needing these extra
checks for buddy merging. So what's wrong?

> Hmm... that's same with me.
>
> Below is similar fix that prevents buddy merging when one of buddy's
> migrate type, but, not both, is MIGRATE_ISOLATE. In fact, I have
> no idea why previous fix (more correct fix) doesn't work for you.
> (It works for me.) But, maybe there is a bug on the fix
> so I make new one which is more general form. Please test it.
>
> Thanks.
>
> ---------->8-------------
> From dd41e348572948d70b935fc24f82c096ff0fb417 Mon Sep 17 00:00:00 2001
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Date: Fri, 4 Mar 2016 13:28:17 +0900
> Subject: [PATCH] mm/cma: fix race
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
> mm/page_alloc.c | 33 +++++++++++++++++++--------------
> 1 file changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c6c38ed..d80d071 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -620,8 +620,8 @@ 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)
> {
> if (!pfn_valid_within(page_to_pfn(buddy)))
> return 0;
> @@ -644,6 +644,20 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
> if (page_zone_id(page) != page_zone_id(buddy))
> return 0;
>
> + if (IS_ENABLED(CONFIG_CMA) &&
> + unlikely(has_isolate_pageblock(zone)) &&
> + unlikely(order >= pageblock_order)) {
> + int page_mt, buddy_mt;
> +
> + page_mt = get_pageblock_migratetype(page);
> + buddy_mt = get_pageblock_migratetype(buddy);
> +
> + if (page_mt != buddy_mt &&
> + (is_migrate_isolate(page_mt) ||
> + is_migrate_isolate(buddy_mt)))
> + return 0;
> + }
> +
> VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
>
> return 1;
> @@ -691,17 +705,8 @@ 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);
>
> @@ -711,7 +716,7 @@ 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))
> break;
> /*
> * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
> @@ -745,7 +750,7 @@ 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)) {
> list_add_tail(&page->lru,
> &zone->free_area[order].free_list[migratetype]);
> goto out;
>