From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3195C433E1 for ; Wed, 15 Jul 2020 03:46:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B94D12074B for ; Wed, 15 Jul 2020 03:46:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728644AbgGODqF (ORCPT ); Tue, 14 Jul 2020 23:46:05 -0400 Received: from out30-131.freemail.mail.aliyun.com ([115.124.30.131]:42584 "EHLO out30-131.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728578AbgGODqF (ORCPT ); Tue, 14 Jul 2020 23:46:05 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01422;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0U2lkO7H_1594784760; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0U2lkO7H_1594784760) by smtp.aliyun-inc.com(127.0.0.1); Wed, 15 Jul 2020 11:46:00 +0800 Date: Wed, 15 Jul 2020 11:46:00 +0800 From: Wei Yang To: Mike Kravetz Cc: Vlastimil Babka , Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/hugetlb: hide nr_nodes in the internal of for_each_node_mask_to_[alloc|free] Message-ID: <20200715034600.GA88314@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200714073404.84863-1-richard.weiyang@linux.alibaba.com> <807a1e32-926b-2882-740b-6484b8dca2b6@suse.cz> <20200714095713.GA86690@L-31X9LVDL-1304.local> <694bb1ac-4f9c-a6a5-7c87-1fc0cdd948a6@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <694bb1ac-4f9c-a6a5-7c87-1fc0cdd948a6@oracle.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 14, 2020 at 02:12:03PM -0700, Mike Kravetz wrote: >On 7/14/20 3:02 AM, Vlastimil Babka wrote: >> On 7/14/20 11:57 AM, Wei Yang wrote: >>> On Tue, Jul 14, 2020 at 11:22:03AM +0200, Vlastimil Babka wrote: >>>> On 7/14/20 11:13 AM, Vlastimil Babka wrote: >>>>> On 7/14/20 9:34 AM, Wei Yang wrote: >>>>>> The second parameter of for_each_node_mask_to_[alloc|free] is a loop >>>>>> variant, which is not used outside of loop iteration. >>>>>> >>>>>> Let's hide this. >>>>>> >>>>>> Signed-off-by: Wei Yang >>>>>> --- >>>>>> mm/hugetlb.c | 38 ++++++++++++++++++++------------------ >>>>>> 1 file changed, 20 insertions(+), 18 deletions(-) >>>>>> >>>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>>> index 57ece74e3aae..9c3d15fb317e 100644 >>>>>> --- a/mm/hugetlb.c >>>>>> +++ b/mm/hugetlb.c >>>>>> @@ -1196,17 +1196,19 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed) >>>>>> return nid; >>>>>> } >>>>>> >>>>>> -#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask) \ >>>>>> - for (nr_nodes = nodes_weight(*mask); \ >>>>>> - nr_nodes > 0 && \ >>>>>> +#define for_each_node_mask_to_alloc(hs, node, mask) \ >>>>>> + int __nr_nodes; \ >>>>>> + for (__nr_nodes = nodes_weight(*mask); \ >>>>> >>>>> The problem with this is that if I use the macro twice in the same block, this >>>>> will redefine __nr_nodes and fail to compile, no? >>>>> In that case it's better to avoid setting up this trap, IMHO. >>>> >>>> Ah, and it will also generate the following warning, if the use of for_each* >>>> macro is not the first thing after variable declarations, but there's another >>>> statement before: >>>> >>>> warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement] >>>> >>>> Instead we should switch to C99 and declare it as "for (int __nr_nodes" :P >>> >>> Hmm... I tried what you suggested, but compiler complains. >>> >>> 'for' loop initial declarations are only allowed in C99 or C11 mode >> >> Yes, by "we should switch to C99" I meant that the kernel kbuild system would >> need to switch. Not a trivial change... >> Without that, I don't see how your patch is possible to do safely. > >Vlastimil, thanks for pointing out future potential issues with this patch. >I likely would have missed that. > >Wei, thanks for taking the time to put together the patch. However, I tend >to agree with Vlastimil's assesment. The cleanup is not worth the risk of >running into issues if someone uses multiple instances of the macro. Yep, thanks all for your feedback. >-- >Mike Kravetz -- Wei Yang Help you, Help me