From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 20 May 2008 16:02:42 +0900 From: KAMEZAWA Hiroyuki Subject: Re: Possible partial miss in pages needed for zone's memory map? Message-Id: <20080520160242.9533c2ee.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20080519231937.5fee7cf7.akpm@linux-foundation.org> References: <87y769f7i4.fsf@saeurebad.de> <20080519231937.5fee7cf7.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Johannes Weiner , Linux Kernel Mailing List , linux-mm@kvack.org List-ID: On Mon, 19 May 2008 23:19:37 -0700 Andrew Morton wrote: > On Sat, 17 May 2008 14:19:15 +0200 Johannes Weiner wrote: > > > Hi, > > > > I stumbled over the following in the zone initialization code. Please > > let me know if I overlooked something here. > > > > hm, no takers. Let's add linux-mm. > > > > > From: Johannes Weiner > > Subject: [PATCH] Don't drop a partial page in a zone's memory map size > > > > In a zone's present pages number, account for all pages occupied by the > > memory map, including a partial. > > > > Signed-off-by: Johannes Weiner > > --- > > > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3378,7 +3378,8 @@ static void __paginginit free_area_init_ > > * is used by this zone for memmap. This affects the watermark > > * and per-cpu initialisations > > */ > > - memmap_pages = (size * sizeof(struct page)) >> PAGE_SHIFT; > > + memmap_pages = > > + PAGE_ALIGN(size * sizeof(struct page)) >> PAGE_SHIFT; > > if (realsize >= memmap_pages) { > > realsize -= memmap_pages; > > printk(KERN_DEBUG > > I looked in there for 30 seconds and collapsed in confusion over which > variables are in which units. > Hmm, size * sizeof(struct page) is multiple of PAGE_SIZE in many case. Becasue "size" is always alinged to (1 << MAX_ORDER -1) (I believe...). ex.) In x86 case, (1 << (MAX_ORDER(11) - 1)) * 4 (sizeof(long)) = (1 << 12) = PAGE_SIZE. But not sure on other archs with various params. I think above fix is correct. Thanks, -Kame -- 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