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 824A9C433E3 for ; Thu, 13 Aug 2020 16:29:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3FEAE20855 for ; Thu, 13 Aug 2020 16:29:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="aLNRnS0+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FEAE20855 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D4FE86B0005; Thu, 13 Aug 2020 12:29:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CFFD96B000C; Thu, 13 Aug 2020 12:29:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C151A6B0022; Thu, 13 Aug 2020 12:29:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0177.hostedemail.com [216.40.44.177]) by kanga.kvack.org (Postfix) with ESMTP id AC4746B0005 for ; Thu, 13 Aug 2020 12:29:06 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 5CF525847 for ; Thu, 13 Aug 2020 16:29:06 +0000 (UTC) X-FDA: 77146079892.13.straw72_0d1531126ff5 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin13.hostedemail.com (Postfix) with ESMTP id 24C7418140B60 for ; Thu, 13 Aug 2020 16:29:06 +0000 (UTC) X-HE-Tag: straw72_0d1531126ff5 X-Filterd-Recvd-Size: 3977 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Thu, 13 Aug 2020 16:29:05 +0000 (UTC) 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) X-Rspamd-Queue-Id: 24C7418140B60 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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