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 <iamjoonsoo.kim@xxxxxxx> > --- > 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 > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>