Received: by 2002:a6b:500f:0:0:0:0:0 with SMTP id e15csp367177iob; Tue, 3 May 2022 20:26:16 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzcX6w06bmVhJbuz3398xYWsFdhhKrs+FkV17AYjp7oFwfoNIq7pbNZf5LQgRSA8vF4s/qj X-Received: by 2002:a17:906:974c:b0:6f4:a205:2b51 with SMTP id o12-20020a170906974c00b006f4a2052b51mr4317118ejy.142.1651634775812; Tue, 03 May 2022 20:26:15 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1651634775; cv=none; d=google.com; s=arc-20160816; b=x+T3TF16c6UQpf2xLPLET6PjAyx3r2Pk5EpflI+45O5IAvorrS8sFuT7wXLhZ/auG8 tOxkYfupDV7o3dCrq4OyAEjIEfr8UOk4KNckv7n93+wqieeVTbglaP1rfG8xsyl22QaH YsZ7+zlZKWItguQwlK5dOo65oyvHZjPQiLh7Oq+6O1WVy9E6SGtCoUWT1vk/20DX77PM Pq9qgpuPxusyjtP2U4tWaNoi0LQDLB2VFHsuQtGz9oj7sK/sNXRdv2rwE3UKxeLOjmV+ eEu0BQiOAaxBM5Xr30qsqwr9zV0MAKPidh/LAldzZqS2GvtZFWGCQUveqi6lDJgNYpOL OfXg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-disposition:mime-version:reply-to :message-id:subject:cc:to:from:date:dkim-signature; bh=Wa8BmtTUEuX2JFAVt4xlQi49ogVICY66/CxQ6lylNXQ=; b=e8vLcGjVTMMqsFkDbpRnNLL+RTvK7VLq/OGpqlvbZEaVEqxRuCI7+m1QUfIwwwybHm Y+E0jywj9LfznTft4MZnQr8A0Fyy5yK4Ld6wuHrusmwZ3I6icM4sIHeQyDVxVjTTQah1 AmyWZ8GwpgXlILzMxjBdj+tQWkcuTVPqK7s1J00C4Z+9/sX5do2wom2UnuAem1PfrYt4 nYeNRUOysLaXVWD1awo31JrcyHTehUu7bqBTzVVfLx0M/19NBiAAv9lh1GPpaIfzmioc FBrsg9Uu7gj2+Um78Qa3YeWPxlW8D1Zdu/wyDmPU5tU1gn5RiI6MC7AgxnIIWpnvEClt gIyw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=j51WGuTq; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Return-Path: Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id m10-20020a056402050a00b00425b6b4802fsi15913650edv.315.2022.05.03.20.25.47; Tue, 03 May 2022 20:26:15 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=j51WGuTq; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239070AbiECQCz (ORCPT + 99 others); Tue, 3 May 2022 12:02:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238803AbiECQCx (ORCPT ); Tue, 3 May 2022 12:02:53 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85AD13C722 for ; Tue, 3 May 2022 08:59:21 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id EE608CE1E2F for ; Tue, 3 May 2022 15:59:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37067C385A4; Tue, 3 May 2022 15:59:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1651593558; bh=XY9ch2qBQz1SEgroJDBDxJ7tbxMsdOzqeG8iF4Vg6NA=; h=Date:From:To:Cc:Subject:Reply-To:From; b=j51WGuTq2KD/fLVJmuUDFZe+OZdWlAv8lR3nxVgu+whTaECowisgCxpMK7kYHvjo7 hMee1gp1pLguQI0tuxugGNPQcOkcl4vX5MpuH2efetRFWh0F6qOkcahZQFDaqnLOBP 90Pgrsy3CtA6Dx/y9sp7axtpqPASAG5tmz6jsoIUv79pV7KPq6V2oh72kM4Y4qVHPw b4OOBDRWHrvs/YLISULk0upIqPoN0nHAJTqylDO/aPa3KjayQ6OnEcLCedZJ0hjh+Z I37cepvKUZKOWILyaTJVa6bXzJHD0sjkB9rarzL2oKySkt3T0cOtWd9rEQv8+hQjbM lsYTkvd69L0qA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 0F0AA5C0115; Tue, 3 May 2022 08:59:13 -0700 (PDT) Date: Tue, 3 May 2022 08:59:13 -0700 From: "Paul E. McKenney" To: liam.howlett@oracle.com, willy@infradead.org, walken.cr@gmail.com, mhocko@suse.com, hannes@cmpxchg.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Memory allocation on speculative fastpaths Message-ID: <20220503155913.GA1187610@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-7.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! Just following up from off-list discussions yesterday. The requirements to allocate on an RCU-protected speculative fastpath seem to be as follows: 1. Never sleep. 2. Never reclaim. 3. Leave emergency pools alone. Any others? If those rules suffice, and if my understanding of the GFP flags is correct (ha!!!), then the following GFP flags should cover this: __GFP_NOMEMALLOC | __GFP_NOWARN Or is this just a fancy way of always returning NULL or some such? ;-) Thanx, Paul