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 1CAC7C4332F for ; Sat, 15 Oct 2022 22:27:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229562AbiJOW1S (ORCPT ); Sat, 15 Oct 2022 18:27:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35982 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229510AbiJOW1R (ORCPT ); Sat, 15 Oct 2022 18:27:17 -0400 Received: from out0.migadu.com (out0.migadu.com [IPv6:2001:41d0:2:267::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1C494003D; Sat, 15 Oct 2022 15:27:15 -0700 (PDT) Message-ID: <5b3c2ccb-4e77-5707-d41a-5a91bd677c8f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1665872833; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jyH/LzULF59OH5GGYkSCeFkBRluBAuYmG36QDeuLDGA=; b=ItVPqsA8nPWYRcgRztZnKGeigQevIb9NNMeUq1fNX+x4UrWR9/a/r4xf9hM1/M/UN/A0FE J0jjez2AWgJo3JWhZKhTKzlqPa+y42b15ojkvYOEoa+ulIkQTOuTTRZJIw0bPYje9gkI6f tYhoEvKW6MGKkq4vtGWr/i4EaGVLM5Y= Date: Sat, 15 Oct 2022 16:27:12 -0600 MIME-Version: 1.0 Subject: Re: [PATCH v2 0/3] Bitmap percentage flushing Content-Language: en-US To: John Stoffel Cc: Song Liu , linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, jonathan.derrick@solidigm.com, jonathanx.sk.derrick@intel.com, Mariusz Tkaczyk References: <20221013224151.300-1-jonathan.derrick@linux.dev> <25417.53318.731340.683540@quad.stoffel.home> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Jonathan Derrick In-Reply-To: <25417.53318.731340.683540@quad.stoffel.home> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On 10/14/2022 3:10 PM, John Stoffel wrote: >>>>>> "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? I'll adjust it to chunk-count-based in the cover letter and make sure it specifies bandwidth. I figured the chunk-count-based was a good way to cover the desired percentage-based feature [1]. [1] https://elixir.bootlin.com/linux/latest/source/drivers/md/md-bitmap.c#L16 > > >> 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. 40% or more of given workload I/Os being bitmap flushes. Will be more clear in v3 > >> 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 >