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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 7D653C0044C for ; Wed, 7 Nov 2018 23:00:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4A68720882 for ; Wed, 7 Nov 2018 23:00:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4A68720882 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728312AbeKHId2 (ORCPT ); Thu, 8 Nov 2018 03:33:28 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:48286 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727744AbeKHId1 (ORCPT ); Thu, 8 Nov 2018 03:33:27 -0500 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 6FCDB941; Wed, 7 Nov 2018 23:00:53 +0000 (UTC) Date: Wed, 7 Nov 2018 15:00:52 -0800 From: Andrew Morton To: Vitaly Wool Cc: Linux-MM , LKML , Oleksiy.Avramchenko@sony.com, Guenter Roeck Subject: Re: [PATCH] z3fold: encode object length in the handle Message-Id: <20181107150052.ed3d26414c3b2f74956a3d42@linux-foundation.org> In-Reply-To: References: <20181025112821.0924423fb9ecc7918896ec2b@gmail.com> <20181025124249.0ba63f1041ed8836ff6e6190@linux-foundation.org> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 29 Oct 2018 13:27:36 +0100 Vitaly Wool wrote: > Hi Andrew, > > Den tors 25 okt. 2018 kl 21:42 skrev Andrew Morton < > akpm@linux-foundation.org>: > > > On Thu, 25 Oct 2018 11:28:21 +0200 Vitaly Wool > > wrote: > > > > > Reclaim and free can race on an object (which is basically ok) but > > > in order for reclaim to be able to map "freed" object we need to > > > encode object length in the handle. handle_to_chunks() is thus > > > introduced to extract object length from a handle and use it during > > > mapping of the last object we couldn't correctly map before. > > > > What are the runtime effects of this change? > > > > I haven't observed any adverse impact with this change used in zswap (and > in fact, this is a bugfix for zswap operation). There is a slight under 1% > impact when z3fold is used with ZRAM but since the support for ZRAM over > zpool is still out of tree, I take it doesn't matter at this point, right? > I mean "runtime effects", not "run time effects" ;) Apart from wishing to document this change fully, I'm trying to understand which kernel version(s) need the fix. To understand that, I need to know the effect upon end-user-visible behaviour. You say it fixes a bug - please describe that bug: how it is triggered, what effect is has, etc. Also, any suggestions as to which kernel versions we should fix is always welcome.