From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752131AbbHCEKL (ORCPT <rfc822;w@1wt.eu>);
	Mon, 3 Aug 2015 00:10:11 -0400
Received: from mga01.intel.com ([192.55.52.88]:13368 "EHLO mga01.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751339AbbHCEKK (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 3 Aug 2015 00:10:10 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.15,598,1432623600"; 
   d="scan'208";a="776510229"
Message-ID: <55BEE99E.8090901@intel.com>
Date: Sun, 02 Aug 2015 21:10:06 -0700
From: Dave Hansen <dave.hansen@intel.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0
MIME-Version: 1.0
To: Xishi Qiu <qiuxishi@huawei.com>
CC: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>,
        Vlastimil Babka <vbabka@suse.cz>, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@suse.cz>, iamjoonsoo.kim@lge.com,
        alexander.h.duyck@redhat.com, sasha.levin@oracle.com,
        Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: add the block to the tail of the list in expand()
References: <55BB4027.7080200@huawei.com> <55BC0392.2070205@intel.com> <55BECC85.7050206@huawei.com>
In-Reply-To: <55BECC85.7050206@huawei.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 08/02/2015 07:05 PM, Xishi Qiu wrote:
>> > Also, this might not do very much good in practice.  If you are
>> > splitting a high-order page, you are doing the split because the
>> > lower-order lists are empty.  So won't that list_add() be to an empty
> 
> I made a mistake, you are right, all the lower-order lists are empty,
> so it is no sense to add to the tail.

I actually tested this experimentally and the lists are not always
empty.  It's probably __rmqueue_smallest() vs. __rmqueue_fallback() logic.

In any case, you might want to double-check.