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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 1CAACC433DF for ; Fri, 31 Jul 2020 20:59:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF15522B42 for ; Fri, 31 Jul 2020 20:59:47 +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="UMB5h2mn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728437AbgGaU7o (ORCPT ); Fri, 31 Jul 2020 16:59:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727053AbgGaU7o (ORCPT ); Fri, 31 Jul 2020 16:59:44 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C69BBC061574 for ; Fri, 31 Jul 2020 13:59:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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=Lf6Tsl2/eoEgie5skYyJMNmAvL2Bjr4XRRNee/YKgpA=; b=UMB5h2mnjeZ1NU4HpmUnHmv/Rd HlcVYUzWJqeRgQ7GmNTDwJKdfVWRmyOvoj2S2q7zuz2PR6kN+5ozMq2Qxr5jP2ervyaxpMjTbw+75 5kfJUxiIIuEUqDIJ6DrYn3opeyfLlOEi40gxdA5EeSnbEjiTgPESdcm7Ppgakn9OsWgXRFCCOOSac dCwfMC7kRA/4TSef8vfpHayLwXM2/0VoUkRqT0y/aTraUF3glixnQNfDJCcC9YNvlAXFt08w4dPp+ bTGtp3vu7Y9sciW02YGMVX9zXrW21edap9a2j/v8WtT3Bj7jI+d0MpZ1GRbITZms9maEJidP5XhI5 qovR2ptw==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1c7p-0002RM-4g; Fri, 31 Jul 2020 20:59:33 +0000 Date: Fri, 31 Jul 2020 21:59:33 +0100 From: Matthew Wilcox To: "Paul E. McKenney" Cc: Andrew Morton , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, hannes@cmpxchg.org, urezki@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: Raw spinlocks and memory allocation Message-ID: <20200731205933.GT23808@casper.infradead.org> References: <20200730231205.GA11265@paulmck-ThinkPad-P72> <20200731133834.517fdfee99b7ed2239f576aa@linux-foundation.org> <20200731204855.GR9247@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200731204855.GR9247@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 31, 2020 at 01:48:55PM -0700, Paul E. McKenney wrote: > On Fri, Jul 31, 2020 at 01:38:34PM -0700, Andrew Morton wrote: > > On Thu, 30 Jul 2020 16:12:05 -0700 "Paul E. McKenney" wrote: > > > > > So, may we add a GFP_ flag that will cause kmalloc() and friends to return > > > NULL when they would otherwise need to acquire their non-raw spinlock? > > > This avoids adding any overhead to the slab-allocator fastpaths, but > > > allows callback invocation to reduce cache misses without having to > > > restructure some existing callers of call_rcu() and potential future > > > callers of kfree_rcu(). > > > > We have eight free gfp_t bits so that isn't a problem. > > Whew!!! ;-) > > > Adding a test-n-branch to the kmalloc() fastpath may well be a concern. > > > > Which of mm/sl?b.c are affected? > > None of them, it turns out. The initial patch will instead directly > invoke __get_free_page(). So we could just leave sl?b.c alone. Isn't that spelled GFP_NOWAIT?