From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755285AbdGKHQR (ORCPT ); Tue, 11 Jul 2017 03:16:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:33111 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753551AbdGKHQQ (ORCPT ); Tue, 11 Jul 2017 03:16:16 -0400 Date: Tue, 11 Jul 2017 09:16:12 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mike.kravetz@oracle.com Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable() Message-ID: <20170711071612.GG24852@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 11-07-17 08:56:04, 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." I though this referred to this check if (vma->vm_next && vma->vm_next->vm_start < end) becuase get_unampped_area with MAP_FIXED doesn't really check anything. It will simply return the given address. Btw. this also rules out find_vma. > > 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. Because it doesn't do anything AFAICS. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id DBBDF6B04CE for ; Tue, 11 Jul 2017 03:16:16 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id x23so29520498wrb.6 for ; Tue, 11 Jul 2017 00:16:16 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id q18si9819424wrb.366.2017.07.11.00.16.15 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 11 Jul 2017 00:16:15 -0700 (PDT) Date: Tue, 11 Jul 2017 09:16:12 +0200 From: Michal Hocko Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable() Message-ID: <20170711071612.GG24852@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <337a8a4c-1f27-7371-409d-6a9f181b3871@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Anshuman Khandual , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mike.kravetz@oracle.com On Tue 11-07-17 08:56:04, 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." I though this referred to this check if (vma->vm_next && vma->vm_next->vm_start < end) becuase get_unampped_area with MAP_FIXED doesn't really check anything. It will simply return the given address. Btw. this also rules out find_vma. > > 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. Because it doesn't do anything AFAICS. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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