From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754553AbdKBLpD (ORCPT ); Thu, 2 Nov 2017 07:45:03 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:39618 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751098AbdKBLpB (ORCPT ); Thu, 2 Nov 2017 07:45:01 -0400 Subject: Re: [PATCH] mm/swap: Use page flags to determine LRU list in __activate_page() To: Vlastimil Babka , Michal Hocko , Anshuman Khandual References: <20171019145657.11199-1-khandual@linux.vnet.ibm.com> <20171019153322.c4uqalws7l7fdzcx@dhcp22.suse.cz> <23110557-b2db-9f4a-d072-ad58fd0c1931@suse.cz> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, shli@kernel.org From: Anshuman Khandual Date: Thu, 2 Nov 2017 17:14:40 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <23110557-b2db-9f4a-d072-ad58fd0c1931@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 17110211-0040-0000-0000-000003E9BA4E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17110211-0041-0000-0000-000025EC452F Message-Id: <40de21c5-9f6e-d34a-6db5-445c43a1266b@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-11-02_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1711020153 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/31/2017 06:15 PM, Vlastimil Babka wrote: > On 10/19/2017 05:33 PM, Michal Hocko wrote: >> On Thu 19-10-17 20:26:57, Anshuman Khandual wrote: >>> Its already assumed that the PageActive flag is clear on the input >>> page, hence page_lru(page) will pick the base LRU for the page. In >>> the same way page_lru(page) will pick active base LRU, once the >>> flag PageActive is set on the page. This change of LRU list should >>> happen implicitly through the page flags instead of being hard >>> coded. >> >> The patch description tells what but it doesn't explain _why_? Does the >> resulting code is better, more optimized or is this a pure readability >> thing? >> >> All I can see is that page_lru is more complex and a large part of it >> can be optimized away which has been done manually here. I suspect the >> compiler can deduce the same thing. > > We shouldn't overestimate the compiler (or the objective conditions it > has) for optimizing stuff away: > > After applying the patch: > > ./scripts/bloat-o-meter swap_before.o mm/swap.o > add/remove: 0/0 grow/shrink: 1/0 up/down: 160/0 (160) > function old new delta > __activate_page 708 868 +160 > Total: Before=13538, After=13698, chg +1.18% > > I don't think we want that, it's not exactly a cold code... Yeah, makes sense.