From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f41.google.com (mail-pa0-f41.google.com [209.85.220.41]) by kanga.kvack.org (Postfix) with ESMTP id DA34C6B0254 for ; Fri, 31 Jul 2015 19:24:06 -0400 (EDT) Received: by pabkd10 with SMTP id kd10so47709992pab.2 for ; Fri, 31 Jul 2015 16:24:06 -0700 (PDT) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTP id e6si13700492pat.29.2015.07.31.16.24.05 for ; Fri, 31 Jul 2015 16:24:06 -0700 (PDT) Message-ID: <55BC0392.2070205@intel.com> Date: Fri, 31 Jul 2015 16:24:02 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [PATCH] mm: add the block to the tail of the list in expand() References: <55BB4027.7080200@huawei.com> In-Reply-To: <55BB4027.7080200@huawei.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Xishi Qiu , Andrew Morton , Mel Gorman , Vlastimil Babka , Johannes Weiner , Michal Hocko , iamjoonsoo.kim@lge.com, alexander.h.duyck@redhat.com, sasha.levin@oracle.com Cc: Linux MM , LKML 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 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