From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f178.google.com (mail-ig0-f178.google.com [209.85.213.178]) by kanga.kvack.org (Postfix) with ESMTP id 30D819003C9 for ; Sun, 2 Aug 2015 22:11:04 -0400 (EDT) Received: by igbpg9 with SMTP id pg9so47276934igb.0 for ; Sun, 02 Aug 2015 19:11:04 -0700 (PDT) Received: from szxga01-in.huawei.com (szxga01-in.huawei.com. [58.251.152.64]) by mx.google.com with ESMTPS id b7si4669572igf.27.2015.08.02.19.11.02 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Sun, 02 Aug 2015 19:11:03 -0700 (PDT) Message-ID: <55BECC85.7050206@huawei.com> Date: Mon, 3 Aug 2015 10:05:57 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [PATCH] mm: add the block to the tail of the list in expand() References: <55BB4027.7080200@huawei.com> <55BC0392.2070205@intel.com> In-Reply-To: <55BC0392.2070205@intel.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Andrew Morton , Mel Gorman , Vlastimil Babka , Johannes Weiner , Michal Hocko , iamjoonsoo.kim@lge.com, alexander.h.duyck@redhat.com, sasha.levin@oracle.com, Linux MM , LKML On 2015/8/1 7:24, Dave Hansen wrote: > On 07/31/2015 02:30 AM, Xishi Qiu wrote: >> __free_one_page() will judge whether the the next-highest order is free, >> then add the block to the tail or not. So when we split large order block, >> add the small block to the tail, it will reduce fragment. > > It's an interesting idea, but what does it do in practice? Can you > measure a decrease in fragmentation? > > Further, the comment above the function says: > * The order of subdivision here is critical for the IO subsystem. > * Please do not alter this order without good reasons and regression > * testing. > > Has there been regression testing? > > 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 Hi Dave, I made a mistake, you are right, all the lower-order lists are empty, so it is no sense to add to the tail. Thanks, Xishi Qiu > list most of the time? Or does the __rmqueue_fallback() > largest->smallest logic dominate? > > . > -- 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