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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 980BCC32750 for ; Tue, 13 Aug 2019 05:26:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 64CC420651 for ; Tue, 13 Aug 2019 05:26:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 64CC420651 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 368076B0005; Tue, 13 Aug 2019 01:26:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 31B8F6B0006; Tue, 13 Aug 2019 01:26:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1B9FF6B0007; Tue, 13 Aug 2019 01:26:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id EF6946B0005 for ; Tue, 13 Aug 2019 01:26:01 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 9E63D180AD7C1 for ; Tue, 13 Aug 2019 05:26:01 +0000 (UTC) X-FDA: 75816268122.06.top48_8bdbdaa849d54 X-HE-Tag: top48_8bdbdaa849d54 X-Filterd-Recvd-Size: 3253 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Tue, 13 Aug 2019 05:26:00 +0000 (UTC) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Aug 2019 22:25:59 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,380,1559545200"; d="scan'208";a="376185850" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga006.fm.intel.com with ESMTP; 12 Aug 2019 22:25:59 -0700 Date: Tue, 13 Aug 2019 13:25:34 +0800 From: Wei Yang To: Matthew Wilcox Cc: Wei Yang , akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mmap.c: rb_parent is not necessary in __vma_link_list Message-ID: <20190813052534.GA17131@richard> Reply-To: Wei Yang References: <20190813032656.16625-1-richardw.yang@linux.intel.com> <20190813033958.GB5307@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190813033958.GB5307@bombadil.infradead.org> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 12, 2019 at 08:39:58PM -0700, Matthew Wilcox wrote: >On Tue, Aug 13, 2019 at 11:26:56AM +0800, Wei Yang wrote: >> Now we use rb_parent to get next, while this is not necessary. >> >> When prev is NULL, this means vma should be the first element in the >> list. Then next should be current first one (mm->mmap), no matter >> whether we have parent or not. >> >> After removing it, the code shows the beauty of symmetry. > >Uhh ... did you test this? > I reboot successfully with this patch. >> @@ -273,12 +273,8 @@ void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma, >> next = prev->vm_next; >> prev->vm_next = vma; >> } else { >> + next = mm->mmap; >> mm->mmap = vma; >> - if (rb_parent) >> - next = rb_entry(rb_parent, >> - struct vm_area_struct, vm_rb); >> - else >> - next = NULL; >> } > >The full context is: > > if (prev) { > next = prev->vm_next; > prev->vm_next = vma; > } else { > mm->mmap = vma; > if (rb_parent) > next = rb_entry(rb_parent, > struct vm_area_struct, vm_rb); > else > next = NULL; > } > >Let's imagine we have a small tree with three ranges in it. > >A: 5-7 >B: 8-10 >C: 11-13 > >I would imagine an rbtree for this case has B at the top with A >to its left and B to its right. > >Now we're going to add range D at 3-4. 'next' should clearly be range A. >It will have NULL prev. Your code is going to make 'B' next, not A. >Right? mm->mmap is not the rb_root. mm->mmap is the first element in the ordered list, if my understanding is correct. -- Wei Yang Help you, Help me