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_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 7D265C282DE for ; Wed, 5 Jun 2019 07:05:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6114C206BA for ; Wed, 5 Jun 2019 07:05:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726959AbfFEHF4 (ORCPT ); Wed, 5 Jun 2019 03:05:56 -0400 Received: from out30-43.freemail.mail.aliyun.com ([115.124.30.43]:52403 "EHLO out30-43.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726933AbfFEHF4 (ORCPT ); Wed, 5 Jun 2019 03:05:56 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R921e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=xiaoguang.wang@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0TTTdodB_1559718352; Received: from 30.5.112.239(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0TTTdodB_1559718352) by smtp.aliyun-inc.com(127.0.0.1); Wed, 05 Jun 2019 15:05:52 +0800 Subject: Re: [RFC] jbd2: add new "stats" proc file To: Theodore Ts'o Cc: linux-ext4@vger.kernel.org, adilger.kernel@dilger.ca References: <20190603124238.9050-1-xiaoguang.wang@linux.alibaba.com> <20190603143801.GA3048@mit.edu> From: Xiaoguang Wang Message-ID: <62a687d1-b5b9-e985-3a48-a1cd284ec4db@linux.alibaba.com> Date: Wed, 5 Jun 2019 15:05:52 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190603143801.GA3048@mit.edu> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org hi, > On Mon, Jun 03, 2019 at 08:42:38PM +0800, Xiaoguang Wang wrote: >> /proc/fs/jbd2/${device}/info only shows whole average statistical >> info about jbd2's life cycle, but it can not show jbd2 info in >> specified time interval and sometimes this capability is very useful >> for trouble shooting. For example, we can not see how rs_locked and >> rs_flushing grows in specified time interval, but these two indexes >> can explain some reasons for app's behaviours. > > We actually had something like this, but we removed it in commit > bf6993276f7: "jbd2: Use tracepoints for history file". The idea was > that you can get the same information using the jbd2_run_tracepoints > > # echo jbd2_run_stats > /sys/kernel/debug/tracing/set_event > # cat /sys/kernel/debug/tracing/trace_pipe > > ... which will produce output like this: > > jbd2/vdg-8-293 [000] ...2 122.822487: jbd2_run_stats: dev 254,96 tid 4403 wait 0 request_delay 0 running 4 locked 0 flushing 0 logging 7 handle_count 98 blocks 3 blocks_logged 4 > jbd2/vdg-8-293 [000] ...2 122.833101: jbd2_run_stats: dev 254,96 tid 4404 wait 0 request_delay 0 running 14 locked 0 flushing 0 logging 4 handle_count 198 blocks 1 blocks_logged 2 > jbd2/vdg-8-293 [000] ...2 122.839325: jbd2_run_stats: dev 254,96 tid 4405 wait > > With eBPF, we should be able to do something even more user friendly. Yes, I'm learning it :) For this patch, it's because we'd like to implement a monitor system based on web to show jbd2 status's change, then for example if buffered write reports high latency and jbd2 rs_locked and rs_flushing also report high value, we may build a connection between buffered write and jbd2. Previously we planned to make above monitor system parse a jbd2 status file provided by kernel,this would be simplest. But ok, we can try to use ebpf. > > BTW, if you are looking to try to optimize jbd2, a good thing to do is > to take a look at jbd2_handle_stats, filtered on ones where the > interval is larger than some cut-off. Ideally, the time between a > handle getting started and stopped should be as small as possible, > because if a transaction is trying to close, an open handle will get > in the way of that, and other CPU's will be stuck waiting for handle > to complete. This means that pre-reading blocks before starting a > handle, etc., is a really good idea. And monitoring jbd2_handle_stats > is a good way to find potential spots to topimize in ext4. Thanks for your detailed explanation and suggestions. Regards, Xiaoguang Wang > > - Ted >