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[192.55.52.120]) by mx.google.com with ESMTPS id e14si41056182pgg.442.2019.08.06.17.32.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 06 Aug 2019 17:32:40 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of richardw.yang@linux.intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of richardw.yang@linux.intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=richardw.yang@linux.intel.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Aug 2019 17:32:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,353,1559545200"; d="scan'208";a="185828104" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by orsmga002.jf.intel.com with ESMTP; 06 Aug 2019 17:32:37 -0700 Date: Wed, 7 Aug 2019 08:32:14 +0800 From: Wei Yang To: Balbir Singh Cc: Wei Yang , akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mmap.c: refine data locality of find_vma_prev Message-ID: <20190807003214.GC24750@richard> Reply-To: Wei Yang References: <20190806081123.22334-1-richardw.yang@linux.intel.com> <20190806105822.GA25354@dev-dsk-sblbir-2a-88e651b2.us-west-2.amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190806105822.GA25354@dev-dsk-sblbir-2a-88e651b2.us-west-2.amazon.com> 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 Tue, Aug 06, 2019 at 10:58:22AM +0000, Balbir Singh wrote: >On Tue, Aug 06, 2019 at 04:11:23PM +0800, Wei Yang wrote: >> When addr is out of the range of the whole rb_tree, pprev will points to >> the biggest node. find_vma_prev gets is by going through the right most >> node of the tree. >> >> Since only the last node is the one it is looking for, it is not >> necessary to assign pprev to those middle stage nodes. By assigning >> pprev to the last node directly, it tries to improve the function >> locality a little. >> >> Signed-off-by: Wei Yang >> --- >> mm/mmap.c | 7 +++---- >> 1 file changed, 3 insertions(+), 4 deletions(-) >> >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 7e8c3e8ae75f..284bc7e51f9c 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -2271,11 +2271,10 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr, >> *pprev = vma->vm_prev; >> } else { >> struct rb_node *rb_node = mm->mm_rb.rb_node; >> - *pprev = NULL; >> - while (rb_node) { >> - *pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb); >> + while (rb_node && rb_node->rb_right) >> rb_node = rb_node->rb_right; >> - } >> + *pprev = rb_node ? NULL >> + : rb_entry(rb_node, struct vm_area_struct, vm_rb); > >Can rb_node ever be NULL? assuming mm->mm_rb.rb_node is not NULL when we >enter here > My bad, it should be *pprev = !rb_node ? NULL : rb_entry(rb_node, struct vm_area_struct, vm_rb); Thanks >Balbir Singh -- Wei Yang Help you, Help me