From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936811AbdIZLAQ (ORCPT ); Tue, 26 Sep 2017 07:00:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:54850 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S934183AbdIZLAP (ORCPT ); Tue, 26 Sep 2017 07:00:15 -0400 Date: Tue, 26 Sep 2017 13:00:12 +0200 From: Michal Hocko To: Vlastimil Babka Cc: Xishi Qiu , Joonsoo Kim , Mel Gorman , Linux MM , LKML , zhong jiang , yeyunfeng , wanghaitao12@huawei.com, "Zhoukang (A)" Subject: Re: [RFC] a question about mlockall() and mprotect() Message-ID: <20170926110012.jiw6plglsyksj5mc@dhcp22.suse.cz> References: <59CA0847.8000508@huawei.com> <20170926081716.xo375arjoyu5ytcb@dhcp22.suse.cz> <59CA125C.8000801@huawei.com> <20170926090255.jmocezs6s3lpd6p4@dhcp22.suse.cz> <59CA1A57.5000905@huawei.com> <59CA1C6E.4010501@huawei.com> <6b38ed08-62cb-97b1-9f16-1fd8e272b137@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6b38ed08-62cb-97b1-9f16-1fd8e272b137@suse.cz> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 26-09-17 11:45:16, Vlastimil Babka wrote: > On 09/26/2017 11:22 AM, Xishi Qiu wrote: > > On 2017/9/26 17:13, Xishi Qiu wrote: > >>> This is still very fuzzy. What are you actually trying to achieve? > >> > >> I don't expect page fault any more after mlock. > >> > > > > Our apps is some thing like RT, and page-fault maybe cause a lot of time, > > e.g. lock, mem reclaim ..., so I use mlock and don't want page fault > > any more. > > Why does your app then have restricted mprotect when calling mlockall() > and only later adjusts the mprotect? Ahh, OK I see what is goging on. So you have PROT_NONE vma at the time mlockall and then later mprotect it something else and want to fault all that memory at the mprotect time? So basically to do --- diff --git a/mm/mprotect.c b/mm/mprotect.c index 6d3e2f082290..b665b5d1c544 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -369,7 +369,7 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev, * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major * fault on access. */ - if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED && + if ((oldflags & (VM_WRITE | VM_LOCKED)) == VM_LOCKED && (newflags & VM_WRITE)) { populate_vma_page_range(vma, start, end, NULL); } -- Michal Hocko SUSE Labs