Hi Joonsoo,
On Tue, Aug 26, 2014 at 05:08:18PM +0900, Joonsoo Kim wrote:
> Current pageblock isolation logic could isolate each pageblock
> individually. This causes freepage accounting problem if freepage with
> pageblock order on isolate pageblock is merged with other freepage on
> normal pageblock. We can prevent merging by restricting max order of
> merging to pageblock order if freepage is on isolate pageblock.
>
> Side-effect of this change is that there could be non-merged buddy
> freepage even if finishing pageblock isolation, because undoing pageblock
> isolation is just to move freepage from isolate buddy list to normal buddy
> list rather than to consider merging. But, I think it doesn't matter
> because 1) almost allocation request are for equal or below pageblock
> order, 2) caller of pageblock isolation will use this freepage so
> freepage will split in any case and 3) merge would happen soon after
> some alloc/free on this and buddy pageblock.
>
> Signed-off-by: Joonsoo Kim <[email protected]>
> ---
> mm/page_alloc.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 809bfd3..8ba9fb0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -570,6 +570,7 @@ static inline void __free_one_page(struct page *page,
> unsigned long combined_idx;
> unsigned long uninitialized_var(buddy_idx);
> struct page *buddy;
> + int max_order = MAX_ORDER;
>
> VM_BUG_ON(!zone_is_initialized(zone));
>
> @@ -580,18 +581,26 @@ static inline void __free_one_page(struct page *page,
> VM_BUG_ON(migratetype == -1);
> if (unlikely(has_isolate_pageblock(zone))) {
> migratetype = get_pfnblock_migratetype(page, pfn);
> - if (is_migrate_isolate(migratetype))
> + 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 = pageblock_order + 1;
When pageblock_order >= max_order, order in the while loop below could
go beyond MAX_ORDER - 1. Or does it never happen?
Thanks,
Naoya Horiguchi
> goto skip_counting;
> + }
> }
> __mod_zone_freepage_state(zone, 1 << order, migratetype);
>
> skip_counting:
> - page_idx = pfn & ((1 << MAX_ORDER) - 1);
> + page_idx = pfn & ((1 << max_order) - 1);
>
> VM_BUG_ON_PAGE(page_idx & ((1 << order) - 1), page);
> VM_BUG_ON_PAGE(bad_range(zone, page), page);
>
> - while (order < MAX_ORDER-1) {
> + 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))
> --
> 1.7.9.5
>
>
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