From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 91AF26B0007 for ; Wed, 27 Jun 2018 03:24:35 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id g16-v6so1048637edq.10 for ; Wed, 27 Jun 2018 00:24:35 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id v8-v6si1706831edi.315.2018.06.27.00.24.34 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 27 Jun 2018 00:24:34 -0700 (PDT) Date: Wed, 27 Jun 2018 09:24:32 +0200 From: Michal Hocko Subject: Re: [RFC v2 PATCH 2/2] mm: mmap: zap pages with read mmap_sem for large mapping Message-ID: <20180627072432.GC32348@dhcp22.suse.cz> References: <1529364856-49589-1-git-send-email-yang.shi@linux.alibaba.com> <1529364856-49589-3-git-send-email-yang.shi@linux.alibaba.com> <3DDF2672-FCC4-4387-9624-92F33C309CAE@gmail.com> <158a4e4c-d290-77c4-a595-71332ede392b@linux.alibaba.com> <20180620071817.GJ13685@dhcp22.suse.cz> <263935d9-d07c-ab3e-9e42-89f73f57be1e@linux.alibaba.com> <20180626074344.GZ2458@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: Peter Zijlstra , Nadav Amit , Matthew Wilcox , ldufour@linux.vnet.ibm.com, Andrew Morton , Ingo Molnar , acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, "open list:MEMORY MANAGEMENT" , linux-kernel@vger.kernel.org On Tue 26-06-18 18:03:34, Yang Shi wrote: > > > On 6/26/18 12:43 AM, Peter Zijlstra wrote: > > On Mon, Jun 25, 2018 at 05:06:23PM -0700, Yang Shi wrote: > > > By looking this deeper, we may not be able to cover all the unmapping range > > > for VM_DEAD, for example, if the start addr is in the middle of a vma. We > > > can't set VM_DEAD to that vma since that would trigger SIGSEGV for still > > > mapped area. > > > > > > splitting can't be done with read mmap_sem held, so maybe just set VM_DEAD > > > to non-overlapped vmas. Access to overlapped vmas (first and last) will > > > still have undefined behavior. > > Acquire mmap_sem for writing, split, mark VM_DEAD, drop mmap_sem. Acquire > > mmap_sem for reading, madv_free drop mmap_sem. Acquire mmap_sem for > > writing, free everything left, drop mmap_sem. > > > > ? > > > > Sure, you acquire the lock 3 times, but both write instances should be > > 'short', and I suppose you can do a demote between 1 and 2 if you care. > > Thanks, Peter. Yes, by looking the code and trying two different approaches, > it looks this approach is the most straight-forward one. Yes, you just have to be careful about the max vma count limit. -- Michal Hocko SUSE Labs