From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp1040.oracle.com ([156.151.31.81]:18237 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752173AbdG1O5m (ORCPT ); Fri, 28 Jul 2017 10:57:42 -0400 Subject: Re: [PATCH v3] Btrfs: add skeleton code for compression heuristic To: dsterba@suse.cz, Adam Borowski , Roman Mamedov , Timofey Titovets , linux-btrfs@vger.kernel.org References: <20170717135258.15865-1-nefelim4ag@gmail.com> <20170717183035.GR2866@twin.jikos.cz> <20170721233749.5175d611@natsu> <20170721210027.3qoexc63zcbbnqxl@angband.pl> <20170724145356.GX2866@twin.jikos.cz> <950a249d-9fb2-103a-0101-d37e6609ba8f@oracle.com> <20170727153653.GO2866@twin.jikos.cz> From: Anand Jain Message-ID: <597B445B.9070107@oracle.com> Date: Fri, 28 Jul 2017 23:04:11 +0900 MIME-Version: 1.0 In-Reply-To: <20170727153653.GO2866@twin.jikos.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 28/07/2017 00:36, David Sterba wrote: > On Mon, Jul 24, 2017 at 11:40:17PM +0800, Anand Jain wrote: >> >>> Eg. files that are already compressed would increase the cpu consumption >>> with compress-force, while they'd be hopefully detected as >>> incompressible with 'compress' and clever heuristics. So the NOCOMPRESS >>> bit would better reflect the status of the file. I thought 'compress' in above, is the compress option. Ah you mean to say compression algo .. got it. Right compress-force for incompressible-data is very expensive. And its also true that compress option for incompressible data is not at all expensive and its only one time. >> current NOCOMPRESS is based on trial and error method and is more >> accurate than heuristic also loss of cpu power is only one time ? > Curreently, force-compress beats everything, so even a file with > NOCOMPRESS will be compressed, all new writes will be passed to the > compression and stored uncompressed eventually. It makes sense to me when you replace NOCOMPRESS with incompressible-data in the above statement. As in my understanding.. You will never have a file with NOCOMPRESS flag if compress-force option is used. > Each time they > compression code will run and fail, so it's not one time. > > Although you can say it's more 'accurate', it's also more expensive. yes. Expensive only in compress-force. >> May be the only opportunity that heuristic can facilitate is at the >> logic to monitor and reset the NOCOMPRESS, as of now there is no >> such a logic. > > The heurictic can be made adaptive, and examine data even for NOCOMPRESS > files, but that's a few steps ahead of where we are now. Nice. Thanks, Anand