From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, page_alloc: don't convert pfn to idx when merging In __free_one_page() we do the buddy merging arithmetics on "page/buddy index", which is just the lower MAX_ORDER bits of pfn. The operations we do that affect the higher bits are bitwise AND and subtraction (in that order), where the final result will be the same with the higher bits left unmasked, as long as these bits are equal for both buddies - which must be true by the definition of a buddy. We can therefore use pfn's directly instead of "index" and skip the zeroing of >MAX_ORDER bits. This can help a bit by itself, although compiler might be smart enough already. It also helps the next patch to avoid page_to_pfn() for memory hole checks. Link: http://lkml.kernel.org/r/20161216120009.20064-1-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/internal.h | 4 ++-- mm/page_alloc.c | 31 ++++++++++++++----------------- mm/page_isolation.c | 8 ++++---- 3 files changed, 20 insertions(+), 23 deletions(-) diff -puN mm/internal.h~mm-page_alloc-dont-convert-pfn-to-idx-when-merging mm/internal.h --- a/mm/internal.h~mm-page_alloc-dont-convert-pfn-to-idx-when-merging +++ a/mm/internal.h @@ -133,9 +133,9 @@ struct alloc_context { * Assumption: *_mem_map is contiguous at least up to MAX_ORDER */ static inline unsigned long -__find_buddy_index(unsigned long page_idx, unsigned int order) +__find_buddy_pfn(unsigned long page_pfn, unsigned int order) { - return page_idx ^ (1 << order); + return page_pfn ^ (1 << order); } extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn, diff -puN mm/page_alloc.c~mm-page_alloc-dont-convert-pfn-to-idx-when-merging mm/page_alloc.c --- a/mm/page_alloc.c~mm-page_alloc-dont-convert-pfn-to-idx-when-merging +++ a/mm/page_alloc.c @@ -787,9 +787,8 @@ static inline void __free_one_page(struc struct zone *zone, unsigned int order, int migratetype) { - unsigned long page_idx; - unsigned long combined_idx; - unsigned long uninitialized_var(buddy_idx); + unsigned long combined_pfn; + unsigned long uninitialized_var(buddy_pfn); struct page *buddy; unsigned int max_order; @@ -802,15 +801,13 @@ static inline void __free_one_page(struc if (likely(!is_migrate_isolate(migratetype))) __mod_zone_freepage_state(zone, 1 << order, migratetype); - page_idx = pfn & ((1 << MAX_ORDER) - 1); - - VM_BUG_ON_PAGE(page_idx & ((1 << order) - 1), page); + VM_BUG_ON_PAGE(pfn & ((1 << order) - 1), page); VM_BUG_ON_PAGE(bad_range(zone, page), page); continue_merging: while (order < max_order - 1) { - buddy_idx = __find_buddy_index(page_idx, order); - buddy = page + (buddy_idx - page_idx); + buddy_pfn = __find_buddy_pfn(pfn, order); + buddy = page + (buddy_pfn - pfn); if (!page_is_buddy(page, buddy, order)) goto done_merging; /* @@ -824,9 +821,9 @@ continue_merging: zone->free_area[order].nr_free--; rmv_page_order(buddy); } - combined_idx = buddy_idx & page_idx; - page = page + (combined_idx - page_idx); - page_idx = combined_idx; + combined_pfn = buddy_pfn & pfn; + page = page + (combined_pfn - pfn); + pfn = combined_pfn; order++; } if (max_order < MAX_ORDER) { @@ -841,8 +838,8 @@ continue_merging: if (unlikely(has_isolate_pageblock(zone))) { int buddy_mt; - buddy_idx = __find_buddy_index(page_idx, order); - buddy = page + (buddy_idx - page_idx); + buddy_pfn = __find_buddy_pfn(pfn, order); + buddy = page + (buddy_pfn - pfn); buddy_mt = get_pageblock_migratetype(buddy); if (migratetype != buddy_mt @@ -867,10 +864,10 @@ done_merging: */ if ((order < MAX_ORDER-2) && pfn_valid_within(page_to_pfn(buddy))) { struct page *higher_page, *higher_buddy; - combined_idx = buddy_idx & page_idx; - higher_page = page + (combined_idx - page_idx); - buddy_idx = __find_buddy_index(combined_idx, order + 1); - higher_buddy = higher_page + (buddy_idx - combined_idx); + combined_pfn = buddy_pfn & pfn; + higher_page = page + (combined_pfn - pfn); + buddy_pfn = __find_buddy_pfn(combined_pfn, order + 1); + higher_buddy = higher_page + (buddy_pfn - combined_pfn); if (page_is_buddy(higher_page, higher_buddy, order + 1)) { list_add_tail(&page->lru, &zone->free_area[order].free_list[migratetype]); diff -puN mm/page_isolation.c~mm-page_alloc-dont-convert-pfn-to-idx-when-merging mm/page_isolation.c --- a/mm/page_isolation.c~mm-page_alloc-dont-convert-pfn-to-idx-when-merging +++ a/mm/page_isolation.c @@ -83,7 +83,7 @@ static void unset_migratetype_isolate(st unsigned long flags, nr_pages; bool isolated_page = false; unsigned int order; - unsigned long page_idx, buddy_idx; + unsigned long pfn, buddy_pfn; struct page *buddy; zone = page_zone(page); @@ -102,9 +102,9 @@ static void unset_migratetype_isolate(st if (PageBuddy(page)) { order = page_order(page); if (order >= pageblock_order) { - page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1); - buddy_idx = __find_buddy_index(page_idx, order); - buddy = page + (buddy_idx - page_idx); + pfn = page_to_pfn(page); + buddy_pfn = __find_buddy_pfn(pfn, order); + buddy = page + (buddy_pfn - pfn); if (pfn_valid_within(page_to_pfn(buddy)) && !is_migrate_isolate_page(buddy)) { _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
