Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755361AbdGKLI4 (ORCPT ); Tue, 11 Jul 2017 07:08:56 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40600 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752577AbdGKLIz (ORCPT ); Tue, 11 Jul 2017 07:08:55 -0400 Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable() To: Vlastimil Babka , Michal Hocko References: <20170710111059.30795-1-khandual@linux.vnet.ibm.com> <20170710134917.GB19645@dhcp22.suse.cz> <20170711060354.GA24852@dhcp22.suse.cz> <4c182da0-6c84-df67-b173-6960fac0544a@suse.cz> <20170711065030.GE24852@dhcp22.suse.cz> <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> Cc: Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mike.kravetz@oracle.com From: Anshuman Khandual Date: Tue, 11 Jul 2017 16:38:46 +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: <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable x-cbid: 17071111-0048-0000-0000-00000253EDBB X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17071111-0049-0000-0000-0000480563FA Message-Id: <8bcc5908-7f0d-ba5c-a484-e0763f9b7664@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-07-11_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000 definitions=main-1707110176 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1023 Lines: 27 On 07/11/2017 12:26 PM, Vlastimil Babka wrote: > On 07/11/2017 08:50 AM, Michal Hocko wrote: >> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote: >>> On 07/11/2017 08:03 AM, Michal Hocko wrote: >>>> >>>> Are you telling me that two if conditions cause more than a second >>>> difference? That sounds suspicious. >>> >>> It's removing also a call to get_unmapped_area(), AFAICS. That means a >>> vma search? >> >> Ohh, right. I have somehow missed that. Is this removal intentional? > > I think it is: "Checking for availability of virtual address range at > the end of the VMA for the incremental size is also reduntant at this > point." > >> The >> changelog is silent about it. > > It doesn't explain why it's redundant, indeed. Unfortunately, the commit > f106af4e90ea ("fix checks for expand-in-place mremap") which added this, > also doesn't explain why it's needed. Its redundant because there are calls to get_unmapped_area() down the line in the function whose failure will anyway fail the expansion of the VMA.