Revert "Bias the placement of kernel pages at lower PFNs"

This reverts commit 5adc5be7cd1bcef6bb64f5255d2a33f20a3cf5be.

Alexey Dobriyan reports that it causes huge slowdowns under some loads,
in his case a "mkfs.ext2" on a 30G partition.  With the placement bias,
the mkfs took over four minutes, with it reverted it's back to about ten
seconds for Alexey.

Reported-and-tested-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index da69d833e0671fe6b8a04b019e47b63c7dcf0f4c..12376ae3f7334e124d488b1d7bc3d291d64e9be1 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -749,23 +749,6 @@ int move_freepages_block(struct zone *zone, struct page *page, int migratetype)
        return move_freepages(zone, start_page, end_page, migratetype);
 }
 
-/* Return the page with the lowest PFN in the list */
-static struct page *min_page(struct list_head *list)
-{
-       unsigned long min_pfn = -1UL;
-       struct page *min_page = NULL, *page;;
-
-       list_for_each_entry(page, list, lru) {
-               unsigned long pfn = page_to_pfn(page);
-               if (pfn < min_pfn) {
-                       min_pfn = pfn;
-                       min_page = page;
-               }
-       }
-
-       return min_page;
-}
-
 /* Remove an element from the buddy allocator from the fallback list */
 static struct page *__rmqueue_fallback(struct zone *zone, int order,
                                                int start_migratetype)
@@ -789,11 +772,8 @@ static struct page *__rmqueue_fallback(struct zone *zone, int order,
                        if (list_empty(&area->free_list[migratetype]))
                                continue;
 
-                       /* Bias kernel allocations towards low pfns */
                        page = list_entry(area->free_list[migratetype].next,
                                        struct page, lru);
-                       if (unlikely(start_migratetype != MIGRATE_MOVABLE))
-                               page = min_page(&area->free_list[migratetype]);
                        area->nr_free--;
 
                        /*