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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 50C50C433DF for ; Sat, 15 Aug 2020 22:02:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 303FD2053B for ; Sat, 15 Aug 2020 22:02:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="L/7ul3MK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728755AbgHOVvZ (ORCPT ); Sat, 15 Aug 2020 17:51:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728694AbgHOVvW (ORCPT ); Sat, 15 Aug 2020 17:51:22 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 055BDC03B3D0; Sat, 15 Aug 2020 01:43:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=pkS7z3ao03yPLdIGYL9tG9q63NVqZ+TpW9PfCZt8oys=; b=L/7ul3MKsMrF7vWFB9Ph0PY0hg +Wrv23G+mNVzExWozkDqWEcrqyDpNmp4bgihjtsFx2veXlJlN6DevE7WbJfH2I1n4oFCN0GuUpzTf VY79AWM7eA+g14iycUVzXdQcho2vLxHb8xDoNgIgcLrYCaM8AcZHV8R9PZFU3X6dIZaQg1iU9NfgY mBy696Lk5WsMxhVOysn+oSmps0iL/ytu7zw6Q4DJIchbCjbhHnVXc3Pq0vI4p8FPu1bdaygCdtEo1 ceCV9N//ZzsESLaouX4qtGOnCnQeDOAA+hTd6Bngcf7lFXG3fdh8MaBQotaqKRhlz1AOPxP8N4wXp pgwrOxuA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k6rm9-0003vH-PT; Sat, 15 Aug 2020 08:42:54 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id C9B6F980C9E; Sat, 15 Aug 2020 10:42:50 +0200 (CEST) Date: Sat, 15 Aug 2020 10:42:50 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: paulmck@kernel.org, Michal Hocko , 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 Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200815084250.GN3982@worktop.programming.kicks-ass.net> References: <20200814180141.GP4295@paulmck-ThinkPad-P72> <87tux4kefm.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tux4kefm.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Sat, Aug 15, 2020 at 01:14:53AM +0200, Thomas Gleixner wrote: > #1 trivial fix is to force switching to an high prio thread or a soft > interrupt which does the allocation Yeah, push the alocation out to another context. I did consider it, but why bother? Also, raising a softirq can't be done from every context, that's a whole new problem. You can do irq_work I suppose, but not all architectures support the self-IPI yet. All in all, it's just more complexity than the fairly trivial __alloc_page_lockless(). Whichever way around, we can't rely on the allocation.