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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 0C358C433E1 for ; Thu, 13 Aug 2020 16:29:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D536320829 for ; Thu, 13 Aug 2020 16:29:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597336146; bh=mYx4fJshJRqk657Xt+birvf0tGGQwEtc93N+G1qkWY8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=tfmwwcMi5uXcpbqOhGSU99fq56fYlaaoUS9gr5CaPZpcgsIpJxdk47Y9JoAJz0t7D g1+PIJ1W58GeqRTRvaOs8lQKS4DG4ZZCCuBYsdNCQ8dflDNqbXw0mlQKjOTpWlRkYl djlVUjFbn/07LIxgSpdcNke8ZBi6WriipdGepaYI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726529AbgHMQ3F (ORCPT ); Thu, 13 Aug 2020 12:29:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:60208 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726142AbgHMQ3F (ORCPT ); Thu, 13 Aug 2020 12:29:05 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9B7AF20658; Thu, 13 Aug 2020 16:29:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597336144; bh=mYx4fJshJRqk657Xt+birvf0tGGQwEtc93N+G1qkWY8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=aLNRnS0+zf6iHufYdbxSvtDFlBhYmFBasFjQbTKkxOCe5q9tBY3BlWgS8OKyqfFMj gYMUr65UldczOkQpIaIkjw1tbgcXPx3QRQl9I0fzEoO9OlvGbeZ2wz6mppnDd/rdxR vQoJWdeuNGJ+1rVlp9BKSGoDEaUw3CL5N7ez0aEI= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 74824352279C; Thu, 13 Aug 2020 09:29:04 -0700 (PDT) Date: Thu, 13 Aug 2020 09:29:04 -0700 From: "Paul E. McKenney" To: Michal Hocko Cc: Thomas Gleixner , Uladzislau Rezki , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko , Peter Zijlstra Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200813162904.GX4295@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200813075027.GD9477@dhcp22.suse.cz> <20200813095840.GA25268@pc636> <874kp6llzb.fsf@nanos.tec.linutronix.de> <20200813133308.GK9477@dhcp22.suse.cz> <87sgcqty0e.fsf@nanos.tec.linutronix.de> <20200813145335.GN9477@dhcp22.suse.cz> <20200813154159.GR4295@paulmck-ThinkPad-P72> <20200813155412.GP9477@dhcp22.suse.cz> <20200813160442.GV4295@paulmck-ThinkPad-P72> <20200813161357.GQ9477@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200813161357.GQ9477@dhcp22.suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 13, 2020 at 06:13:57PM +0200, Michal Hocko wrote: > On Thu 13-08-20 09:04:42, Paul E. McKenney wrote: > > On Thu, Aug 13, 2020 at 05:54:12PM +0200, Michal Hocko wrote: > [...] > > > If the whole bailout is guarded by CONFIG_PREEMPT_RT specific atomicity > > > check then there is no functional problem - GFP_RT_SAFE would still be > > > GFP_NOWAIT so functional wise the allocator will still do the right > > > thing. > > > > Perhaps it was just me getting confused, early hour Pacific Time and > > whatever other excuses might apply. But I thought that you still had > > an objection to GFP_RT_SAFE based on changes in allocator semantics for > > other users. > > There is still that problem with lockdep complaining about raw->regular > spinlock on !PREEMPT_RT that would need to get resolved somehow. Thomas > is not really keen on adding some lockdep annotation mechanism and > unfortunatelly I do not have a different idea how to get rid of those. OK. So the current situation requires a choice between these these alternatives, each of which has shortcomings that have been mentioned earlier in this thread: 1. Prohibit invoking allocators from raw atomic context, such as when holding a raw spinlock. 2. Adding a GFP_ flag. 3. Reusing existing GFP_ flags/values/whatever to communicate the raw-context information that was to be communicated by the new GFP_ flag. 4. Making lockdep forgive acquiring spinlocks while holding raw spinlocks, but only in CONFIG_PREEMPT_NONE=y kernels. Am I missing anything? Thanx, Paul