On Mon, Sep 06, 2010 at 02:42:28PM +0900, KAMEZAWA Hiroyuki wrote:
>
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> next_active_pageblock() is for finding next _used_ freeblock. It skips
> several blocks when it finds there are a chunk of free pages lager than
> pageblock. But it has 2 bugs.
>
> 1. We have no lock. page_order(page) - pageblock_order can be minus.
> 2. pageblocks_stride += is wrong. it should skip page_order(p) of pages.
>
> CC: stable@xxxxxxxxxx
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> mm/memory_hotplug.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> Index: kametest/mm/memory_hotplug.c
> ===================================================================
> --- kametest.orig/mm/memory_hotplug.c
> +++ kametest/mm/memory_hotplug.c
> @@ -584,19 +584,19 @@ static inline int pageblock_free(struct
> /* Return the start of the next active pageblock after a given page */
> static struct page *next_active_pageblock(struct page *page)
> {
> - int pageblocks_stride;
> -
> /* Ensure the starting page is pageblock-aligned */
> BUG_ON(page_to_pfn(page) & (pageblock_nr_pages - 1));
>
> - /* Move forward by at least 1 * pageblock_nr_pages */
> - pageblocks_stride = 1;
> -
> /* If the entire pageblock is free, move to the end of free page */
> - if (pageblock_free(page))
> - pageblocks_stride += page_order(page) - pageblock_order;
> + if (pageblock_free(page)) {
> + int order;
> + /* be careful. we don't have locks, page_order can be changed.*/
> + order = page_order(page);
> + if (order > pageblock_order)
> + return page + (1 << order);
> + }
As you note in your changelog, page_order() is unsafe because we do not have
the zone lock but you don't check if order is somewhere between pageblock_order
and MAX_ORDER_NR_PAGES. How is this safer?
>
> - return page + (pageblocks_stride * pageblock_nr_pages);
> + return page + pageblock_nr_pages;
> }
>
> /* Checks if this range of memory is likely to be hot-removable. */
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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