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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 823D8C28CBC for ; Sat, 9 May 2020 17:54:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BA7E24954 for ; Sat, 9 May 2020 17:54:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728323AbgEIRyw (ORCPT ); Sat, 9 May 2020 13:54:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:55210 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726214AbgEIRyv (ORCPT ); Sat, 9 May 2020 13:54:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id D8F4DAC26; Sat, 9 May 2020 17:54:52 +0000 (UTC) Date: Sat, 9 May 2020 19:54:48 +0200 From: Joerg Roedel To: Peter Zijlstra Cc: Joerg Roedel , x86@kernel.org, hpa@zytor.com, Dave Hansen , Andy Lutomirski , rjw@rjwysocki.net, Arnd Bergmann , Andrew Morton , Steven Rostedt , Vlastimil Babka , Michal Hocko , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 0/7] mm: Get rid of vmalloc_sync_(un)mappings() Message-ID: <20200509175448.GW8135@suse.de> References: <20200508144043.13893-1-joro@8bytes.org> <20200508192000.GB2957@hirez.programming.kicks-ass.net> <20200508213407.GT8135@suse.de> <20200509092516.GC2957@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200509092516.GC2957@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Sat, May 09, 2020 at 11:25:16AM +0200, Peter Zijlstra wrote: > Right; it's just that the moment you do trigger it, it'll iterate that > pgd_list and that is potentially huge. Then again, that's not a new > problem. > > I suppose we can deal with it if/when it becomes an actual problem. > > I had a quick look and I think it might be possible to make it an RCU > managed list. We'd have to remove the pgd_list entry in > put_task_struct_rcu_user(). Then we can play games in sync_global_*() > and use RCU iteration. New tasks (which can be missed in the RCU > iteration) will already have a full clone of the PGD anyway. Right, it should not be that difficult to rcu-protect the pgd-list, but we can try that when it actually becomes a problem. Joerg