From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id DFF556B0003 for ; Sat, 30 Jun 2018 00:26:35 -0400 (EDT) Received: by mail-pl0-f69.google.com with SMTP id f5-v6so6077629plf.18 for ; Fri, 29 Jun 2018 21:26:35 -0700 (PDT) Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com. [115.124.30.132]) by mx.google.com with ESMTPS id m3-v6si11277947plt.71.2018.06.29.21.26.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 Jun 2018 21:26:34 -0700 (PDT) Subject: Re: [RFC v3 PATCH 4/5] mm: mmap: zap pages with read mmap_sem for large mapping References: <1530311985-31251-1-git-send-email-yang.shi@linux.alibaba.com> <1530311985-31251-5-git-send-email-yang.shi@linux.alibaba.com> <20180629183501.9e30c26135f11853245c56c7@linux-foundation.org> <084aeccb-2c54-2299-8bf0-29a10cc0186e@linux.alibaba.com> <20180629201547.5322cfc4b52d19a0443daec2@linux-foundation.org> From: Yang Shi Message-ID: Date: Fri, 29 Jun 2018 21:26:23 -0700 MIME-Version: 1.0 In-Reply-To: <20180629201547.5322cfc4b52d19a0443daec2@linux-foundation.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: mhocko@kernel.org, willy@infradead.org, ldufour@linux.vnet.ibm.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, tglx@linutronix.de, hpa@zytor.com, linux-mm@kvack.org, x86@kernel.org, linux-kernel@vger.kernel.org On 6/29/18 8:15 PM, Andrew Morton wrote: > On Fri, 29 Jun 2018 19:28:15 -0700 Yang Shi wrote: > >> >>> we're adding a bunch of code to 32-bit kernels which will never be >>> executed. >>> >>> I'm thinking it would be better to be much more explicit with "#ifdef >>> CONFIG_64BIT" in this code, rather than relying upon the above magic. >>> >>> But I tend to think that the fact that we haven't solved anything on >>> locked vmas or on uprobed mappings is a shostopper for the whole >>> approach :( >> I agree it is not that perfect. But, it still could improve the most use >> cases. > Well, those unaddressed usecases will need to be fixed at some point. Yes, definitely. > What's our plan for that? As I mentioned in the earlier email, locked and hugetlb cases might be able to be solved by separating vm_flags update and actual unmap. I will look into it further later. From my point of view, uprobe mapping sounds not that vital. > > Would one of your earlier designs have addressed all usecases? I > expect the dumb unmap-a-little-bit-at-a-time approach would have? Yes. The v1 design does unmap with holding write map_sem. So, the vm_flags update is not a problem. Thanks, Yang > >> For the locked vmas and hugetlb vmas, unmapping operations need modify >> vm_flags. But, I'm wondering we might be able to separate unmap and >> vm_flags update. Because we know they will be unmapped right away, the >> vm_flags might be able to be updated in write mmap_sem critical section >> before the actual unmap is called or after it. This is just off the top >> of my head. >> >> For uprobed mappings, I'm not sure how vital it is to this case. >> >> Thanks, >> Yang >>