From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26EC3C433E0 for ; Sun, 2 Aug 2020 11:25:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0EB082075A for ; Sun, 2 Aug 2020 11:25:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728043AbgHBLZc (ORCPT ); Sun, 2 Aug 2020 07:25:32 -0400 Received: from relay7-d.mail.gandi.net ([217.70.183.200]:58157 "EHLO relay7-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726578AbgHBLZb (ORCPT ); Sun, 2 Aug 2020 07:25:31 -0400 X-Originating-IP: 180.110.142.179 Received: from localhost (unknown [180.110.142.179]) (Authenticated sender: fly@kernel.page) by relay7-d.mail.gandi.net (Postfix) with ESMTPSA id 64DFD20007; Sun, 2 Aug 2020 11:24:54 +0000 (UTC) Date: Sun, 2 Aug 2020 19:23:47 +0800 From: Pengfei Li To: Daniel Jordan Cc: Hugh Dickins , akpm@linux-foundation.org, bmt@zurich.ibm.com, dledford@redhat.com, willy@infradead.org, vbabka@suse.cz, kirill.shutemov@linux.intel.com, jgg@ziepe.ca, alex.williamson@redhat.com, cohuck@redhat.com, dbueso@suse.de, jglisse@redhat.com, jhubbard@nvidia.com, ldufour@linux.ibm.com, Liam.Howlett@oracle.com, peterz@infradead.org, cl@linux.com, jack@suse.cz, rientjes@google.com, walken@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, fly@kernel.page Subject: Re: [PATCH 2/2] mm, util: account_locked_vm() does not hold mmap_lock Message-ID: <20200802192347.534ece64.fly@kernel.page> In-Reply-To: <20200730205705.ityqlyeswzo5dkow@ca-dmjordan1.us.oracle.com> References: <20200726080224.205470-1-fly@kernel.page> <20200726080224.205470-2-fly@kernel.page> <20200730205705.ityqlyeswzo5dkow@ca-dmjordan1.us.oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 30 Jul 2020 16:57:05 -0400 Daniel Jordan wrote: > On Wed, Jul 29, 2020 at 12:21:11PM -0700, Hugh Dickins wrote: > > On Sun, 26 Jul 2020, Pengfei Li wrote: > > > > > Since mm->locked_vm is already an atomic counter, > > > account_locked_vm() does not need to hold mmap_lock. > > > > I am worried that this patch, already added to mmotm, along with its > > 1/2 making locked_vm an atomic64, might be rushed into v5.9 with > > just that two-line commit description, and no discussion at all. > > > > locked_vm belongs fundamentally to mm/mlock.c, and the lock to guard > > it is mmap_lock; and mlock() has some complicated stuff to do under > > that lock while it decides how to adjust locked_vm. > > > > It is very easy to convert an unsigned long to an atomic64_t, but > > "atomic read, check limit and do stuff, atomic add" does not give > > the same guarantee as holding the right lock around it all. > > Yes, this is why I withdrew my attempt to do something similar last > year, I didn't want to make the accounting racy. Stack and heap > growing and mremap would be affected in addition to mlock. > > It'd help to hear more about the motivation for this. > Thanks for your comments. My motivation is to allow mm related counters to be safely read and written without holding mmap_lock. But sorry i didn't do well. -- Pengfei