From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f200.google.com (mail-qt0-f200.google.com [209.85.216.200]) by kanga.kvack.org (Postfix) with ESMTP id 03F8F6B0069 for ; Wed, 12 Oct 2016 04:45:23 -0400 (EDT) Received: by mail-qt0-f200.google.com with SMTP id m5so31858364qtb.3 for ; Wed, 12 Oct 2016 01:45:23 -0700 (PDT) Received: from sender153-mail.zoho.com (sender153-mail.zoho.com. [74.201.84.153]) by mx.google.com with ESMTPS id n66si3334083qka.157.2016.10.12.01.45.22 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 12 Oct 2016 01:45:22 -0700 (PDT) Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix memory leakage issue when allocate a odd alignment area References: <20161011172228.GA30403@dhcp22.suse.cz> <7649b844-cfe6-abce-148e-1e2236e7d443@zoho.com> <20161012065332.GA9504@dhcp22.suse.cz> <57FDE531.7060003@zoho.com> <20161012082538.GC17128@dhcp22.suse.cz> From: zijun_hu Message-ID: <57FDF7EF.6070606@zoho.com> Date: Wed, 12 Oct 2016 16:44:31 +0800 MIME-Version: 1.0 In-Reply-To: <20161012082538.GC17128@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, zijun_hu@htc.com, tj@kernel.org, akpm@linux-foundation.org, cl@linux.com On 10/12/2016 04:25 PM, Michal Hocko wrote: > On Wed 12-10-16 15:24:33, zijun_hu wrote: >> On 10/12/2016 02:53 PM, Michal Hocko wrote: >>> On Wed 12-10-16 08:28:17, zijun_hu wrote: >>>> On 2016/10/12 1:22, Michal Hocko wrote: >>>>> On Tue 11-10-16 21:24:50, zijun_hu wrote: >>>>>> From: zijun_hu >>>>>> >> should we have a generic discussion whether such patches which considers >> many boundary or rare conditions are necessary. > > In general, I believe that kernel internal interfaces which have no > userspace exposure shouldn't be cluttered with sanity checks. > you are right and i agree with you. but there are many internal interfaces perform sanity checks in current linux sources >> i found the following code segments in mm/vmalloc.c >> static struct vmap_area *alloc_vmap_area(unsigned long size, >> unsigned long align, >> unsigned long vstart, unsigned long vend, >> int node, gfp_t gfp_mask) >> { >> ... >> >> BUG_ON(!size); >> BUG_ON(offset_in_page(size)); >> BUG_ON(!is_power_of_2(align)); > > See a recent Linus rant about BUG_ONs. These BUG_ONs are quite old and > from a quick look they are even unnecessary. So rather than adding more > of those, I think removing those that are not needed is much more > preferred. > i notice that, and the above code segments is used to illustrate that input parameter checking is necessary sometimes >> should we make below declarations as conventions >> 1) when we say 'alignment', it means align to a power of 2 value >> for example, aligning value @v to @b implicit @v is power of 2 >> , align 10 to 4 is 12 > > alignment other than power-of-two makes only very limited sense to me. > you are right and i agree with you. >> 2) when we say 'round value @v up/down to boundary @b', it means the >> result is a times of @b, it don't requires @b is a power of 2 > i will write to linus to ask for opinions whether we should declare the meaning of 'align' and 'round up/down' formally and whether such patches are necessary -- 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