From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by ug-out-1314.google.com with SMTP id s2so1539171uge for ; Mon, 18 Dec 2006 19:01:36 -0800 (PST) Message-ID: <6d6a94c50612181901m1bfd9d1bsc2d9496ab24eb3f8@mail.gmail.com> Date: Tue, 19 Dec 2006 11:01:36 +0800 From: Aubrey Subject: [RFC][PATCH] Fix area->nr_free-- went (-1) issue in buddy system MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Hi all, When I setup two zones (NORMAL and DMA) in my system, I got the following wired result from /proc/buddyinfo. ----------------------------------------------------------------------------------------- root:~> cat /proc/buddyinfo Node 0, zone DMA 2 1 2 1 1 0 0 1 1 2 2 0 0 0 Node 0, zone Normal 1 1 1 1 1 1 0 0 4294967295 0 4294967295 2 0 0 ----------------------------------------------------------------------------------------- As you see, two area->nr_free went -1. After dig into the code, I found the problem is in the fun __free_one_page() when the kernel boot up call free_all_bootmem(). If two zones setup, it's possible NORMAL zone merged a block whose order =8 at the first time(this time zone[NORMA]->free_area[8].nr_free = 0) and found its buddy in the DMA zone. So the two blocks will be merged and area->nr_free went to -1. My proposed patch is as follows: Signed-off-by: Aubrey Li --------------------------------------------------------------------------------------------------- --- page_alloc.c.orig 2006-12-19 10:45:25.000000000 +0800 +++ page_alloc.c 2006-12-19 10:44:48.000000000 +0800 @@ -407,7 +407,8 @@ static inline void __free_one_page(struc list_del(&buddy->lru); area = zone->free_area + order; - area->nr_free--; + if (area->nr_free > 0) + area->nr_free--; rmv_page_order(buddy); combined_idx = __find_combined_index(page_idx, order); page = page + (combined_idx - page_idx); ---------------------------------------------------------------------------------------------------- Any comments? Thanks, -Aubrey -- 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