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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AF434C43217 for ; Fri, 14 Oct 2022 21:19:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229832AbiJNVTT (ORCPT ); Fri, 14 Oct 2022 17:19:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229826AbiJNVTR (ORCPT ); Fri, 14 Oct 2022 17:19:17 -0400 X-Greylist: delayed 518 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Fri, 14 Oct 2022 14:19:10 PDT Received: from mail.stoffel.org (mail.stoffel.org [172.104.24.175]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 647D71D29AC; Fri, 14 Oct 2022 14:19:09 -0700 (PDT) Received: from quad.stoffel.org (068-116-170-226.res.spectrum.com [68.116.170.226]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by mail.stoffel.org (Postfix) with ESMTPSA id 1A24F1E668; Fri, 14 Oct 2022 17:10:31 -0400 (EDT) Received: by quad.stoffel.org (Postfix, from userid 1000) id B8C27A7F96; Fri, 14 Oct 2022 17:10:30 -0400 (EDT) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <25417.53318.731340.683540@quad.stoffel.home> Date: Fri, 14 Oct 2022 17:10:30 -0400 From: "John Stoffel" To: Jonathan Derrick Cc: Song Liu , , , jonathan.derrick@solidigm.com, jonathanx.sk.derrick@intel.com, Mariusz Tkaczyk Subject: Re: [PATCH v2 0/3] Bitmap percentage flushing In-Reply-To: <20221013224151.300-1-jonathan.derrick@linux.dev> References: <20221013224151.300-1-jonathan.derrick@linux.dev> X-Mailer: VM 8.2.0b under 27.1 (x86_64-pc-linux-gnu) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>>>> "Jonathan" == Jonathan Derrick writes: > This introduces a percentage-flushing mechanism that works in-tandem to the > mdadm delay timer. The percentage argument is based on the number of chunks > dirty (rather than percentage), due to large drives requiring smaller and > smaller percentages (eg, 32TB drives-> 1% is 320GB). I've been reading and re-reading this and I still don't understand what you're saying here. You say you're adding a percentage based mechanism, but then you say it's based on chunk counts, not percentages. I think you need to clean this up and re-word it. Maybe you're trying to say that you only take a percentage of the available write bandwidth per second or something like that? > This set hopes to provide a way to make the bitmap flushing more consistent. It > was observed that a synchronous, random write qd1 workload, could make bitmap > writes easily become almost half of the I/O. And in similar workloads with > different timing, it was several minutes between bitmap updates. This is too > inconsistent to be reliable. > This first and second patches adds the flush_threshold parameter. The default > value of 0 defines the default behavior: unplugging immediately just as before. > With a flush-threshold value of 1, it becomes more consistent and paranoid, > flushing on nearly every I/O, leading to a 40% or greater situation. From What situation? Please be more clear here. > there, the flush_threshold can be defined higher for those situations where > power loss is rare and full resync can be tolerated. > The third patch converts the daemon worker to an actual timer. This makes it > more consistent and removes some ugly code. > Jonathan Derrick (3): > md/bitmap: Add chunk-threshold unplugging > md/bitmap: Add sysfs interface for flush threshold > md/bitmap: Convert daemon_work to proper timer > Documentation/admin-guide/md.rst | 5 ++ > drivers/md/md-bitmap.c | 98 +++++++++++++++++++++++++------- > drivers/md/md-bitmap.h | 4 +- > drivers/md/md.c | 9 ++- > drivers/md/md.h | 2 + > 5 files changed, 93 insertions(+), 25 deletions(-) > -- > 2.31.1