From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id 53D8C6B0047 for ; Mon, 6 Sep 2010 09:39:31 -0400 (EDT) Date: Mon, 6 Sep 2010 14:39:15 +0100 From: Mel Gorman Subject: Re: [BUGFIX][PATCH 1/3] memory hotplug: fix next block calculation in is_removable Message-ID: <20100906133914.GL8384@csn.ul.ie> References: <20100906144019.946d3c49.kamezawa.hiroyu@jp.fujitsu.com> <20100906144228.4ee5a738.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100906144228.4ee5a738.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , fengguang.wu@intel.com, "akpm@linux-foundation.org" , andi.kleen@intel.com, Dave Hansen , stable@kernel.org List-ID: On Mon, Sep 06, 2010 at 02:42:28PM +0900, KAMEZAWA Hiroyuki wrote: > > From: KAMEZAWA Hiroyuki > > 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@kernel.org > Signed-off-by: KAMEZAWA Hiroyuki > --- > 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org