From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx106.postini.com [74.125.245.106]) by kanga.kvack.org (Postfix) with SMTP id 5D1C66B0034 for ; Wed, 31 Jul 2013 12:56:16 -0400 (EDT) Message-ID: <51F9419F.6070306@intel.com> Date: Wed, 31 Jul 2013 09:55:59 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [PATCH] mm/hotplug: remove unnecessary BUG_ON in __offline_pages() References: <51F761E7.5090403@huawei.com> In-Reply-To: <51F761E7.5090403@huawei.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Xishi Qiu Cc: linux-mm@kvack.org, LKML , Andrew Morton , KAMEZAWA Hiroyuki On 07/29/2013 11:49 PM, Xishi Qiu wrote: > I think we can remove "BUG_ON(start_pfn >= end_pfn)" in __offline_pages(), > because in memory_block_action() "nr_pages = PAGES_PER_SECTION * sections_per_block" > is always greater than 0. ... > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1472,7 +1472,6 @@ static int __ref __offline_pages(unsigned long start_pfn, > struct zone *zone; > struct memory_notify arg; > > - BUG_ON(start_pfn >= end_pfn); > /* at least, alignment against pageblock is necessary */ > if (!IS_ALIGNED(start_pfn, pageblock_nr_pages)) > return -EINVAL; I think you're saying that you don't see a way to hit this BUG_ON() in practice. That does appear to be true, unless sections_per_block ended up 0 or negative. The odds of getting in to this code if 'sections_per_block' was bogus are pretty small. Or, is this a theoretical thing that folks might run in to when adding new features or developing? It's in a cold path and the cost of the check is miniscule. The original author (cc'd) also saw a need to put this in probably because he actually ran in to this. In any case, it looks fairly safe to me: Reviewed-by: Dave Hansen -- 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