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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 02C6FC433E0 for ; Mon, 15 Jun 2020 20:04:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA849207DD for ; Mon, 15 Jun 2020 20:04:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592251468; bh=HpSZ+6XhbkSlkxONu9hFhrcjACPI8H0WHNJT01UGSnM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=E4JW6jF6YrnFGv/5jbnR9Vvmy2+iVAiu7D9Ea92WTmBMdnZYmN2SidWlwU5Dafcle GTlaoQ1moyycPXgsscVzqoaGFxuXY7CrYTqN0buNn0kc39xaaU/EL/xBWTyo38RFvd +mZD+EPr0+YQfRujTslW0ZJ8q+RDkH0NesmUF06g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729836AbgFOUE2 (ORCPT ); Mon, 15 Jun 2020 16:04:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:45990 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728773AbgFOUE2 (ORCPT ); Mon, 15 Jun 2020 16:04:28 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 19B072071A; Mon, 15 Jun 2020 20:04:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592251467; bh=HpSZ+6XhbkSlkxONu9hFhrcjACPI8H0WHNJT01UGSnM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=07mSqnzCcPF/Z4fkqrmDv/psU2Xh/EzRPRe7JWL1rPiTclrgNPMz6Ll2G92DJH1hS mx7tZDSgJ9546Wa122WpGpdkf6U82ejgmVnKnGNe6uX74zvIskjhKVjg/FMeLsFLSl jQfhL6AaTgtcMqPI+Ya3zvOHhkoMqijmXVJzvs7Y= Date: Mon, 15 Jun 2020 22:04:22 +0200 From: Greg Kroah-Hartman To: Linus Torvalds Cc: stable Subject: Re: Please add 17839856fd58 to the stable queue Message-ID: <20200615200422.GA206959@kroah.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Jun 15, 2020 at 12:18:48PM -0700, Linus Torvalds wrote: > Commit 17839856fd58 ("gup: document and work around "COW can break > either way" issue") is a real fix, but wasn't marked for stable > because I wanted it to get more coverage testing in mainline first. > Not because the patch is all that complex or scary, but because I was > worried we'd find some odd case where it would make things slower by > triggering the GUP slowpath much more often due to people doing odd > things. > > It turns out my worry seems to have been misplaced. The kernel test > robot did indeed trigger a case where this made a big difference, but > rather than being bad, it improved the odd corner-case test-case > performance by a factor of 20x by breaking the COW and triggering the > fast-case code that way, rather than the other way around. > > See > > https://lore.kernel.org/lkml/20200611040453.GK12456@shao2-debian/ > > for details. > > So that commit fixes a bug, isn't expected to really make any > difference on any sane workload, and can apparently help the crazy > cases by a huge amount. Let's just push it to stable.. Will go do that now, was waiting to see if this caused any problems, glad to see it hasn't. greg k-h