From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id 353A66B0008 for ; Tue, 27 Mar 2018 10:43:23 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id g13so11658059wrh.23 for ; Tue, 27 Mar 2018 07:43:23 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id y64si1131218wmg.164.2018.03.27.07.43.21 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 27 Mar 2018 07:43:21 -0700 (PDT) Date: Tue, 27 Mar 2018 16:43:20 +0200 From: Michal Hocko Subject: Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Message-ID: <20180327144320.GI5652@dhcp22.suse.cz> References: <1522088439-105930-1-git-send-email-yang.shi@linux.alibaba.com> <20180327062939.GV5652@dhcp22.suse.cz> <20180327143122.rjgxjoj2adzvfck2@mguzik> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327143122.rjgxjoj2adzvfck2@mguzik> Sender: owner-linux-mm@kvack.org List-ID: To: Mateusz Guzik Cc: Yang Shi , adobriyan@gmail.com, willy@infradead.org, gorcunov@openvz.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue 27-03-18 16:31:23, Mateusz Guzik wrote: > On Tue, Mar 27, 2018 at 08:29:39AM +0200, Michal Hocko wrote: > > On Tue 27-03-18 02:20:39, Yang Shi wrote: > > [...] > > The patch looks reasonable to me. Maybe it would be better to be more > > explicit about the purpose of the patch. As others noticed, this alone > > wouldn't solve the mmap_sem contention issues. I _think_ that if you > > were more explicit about the mmap_sem abuse it would trigger less > > questions. > > > > >From what I gather even with other fixes the kernel will still end up > grabbing the semaphore. In this case I don't see what's the upside of > adding the spinlock for args. The downside is growth of mm_struct. Because accessing the specific address in the address space can be later changed to use a more fine-grained locking. There are people experimenting with range locking. These mmap_sem abusers, on the other hand, will require the full range lock without a good reason. So it is really worth it to remove them and replace by a more fine grained locking. If the mm_struct grow is a real concern (I haven't checked that) then we can use a set of hashed locks or something else. -- Michal Hocko SUSE Labs