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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 3E4E5C49EA4 for ; Mon, 21 Jun 2021 09:20:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 25830610A3 for ; Mon, 21 Jun 2021 09:20:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230445AbhFUJWq (ORCPT ); Mon, 21 Jun 2021 05:22:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230403AbhFUJWm (ORCPT ); Mon, 21 Jun 2021 05:22:42 -0400 Received: from mail-qk1-x730.google.com (mail-qk1-x730.google.com [IPv6:2607:f8b0:4864:20::730]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 08CB2C0617A8 for ; Mon, 21 Jun 2021 02:20:25 -0700 (PDT) Received: by mail-qk1-x730.google.com with SMTP id q64so22302313qke.7 for ; Mon, 21 Jun 2021 02:20:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=Thh2opi8YGKKCEfU6ECwo8lT/xNy33vFpN+m6aUkk70=; b=Sfu8uTdvW0jrc71YyHyh5FMxfTEEBAQndnCmL6dQ9ergOHCUENc4bR+FFIUDYLUhx3 6MVCVL4fiUOi7VRwE8zX6GW59jCNTh1AdczkRBo10bRNom0MTrH+WE708COsy07lfGFW H8+VH1OBwO59X7fKIzk1lSwPLEQa8KDVqe0l7VQeQRw/GW27lrUnjv09l6yqP9hnId9w EMoVCF2OFTsozX5VTg56eaz8EEo8oChfisqzr7XClOLrGkZpTcY9hlznx5PpTbpPFzNs G7Y6GDl4k78MujFJ/riPoKEavpNecta+tgHkI3yPE9JF6XmS0wrwp5Dxi8ePB9uHRAXq XVXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=Thh2opi8YGKKCEfU6ECwo8lT/xNy33vFpN+m6aUkk70=; b=E0dox4ls1TLPIUa/XPlg0SVg7IyGOiin2/aebzYMf/ypfKmaY6LIDEqnYkF7neUThp 9pyyYcXTys67mf83/Ch+xrTLpiSvSDm+mqJIxQCD26dSrrXEqBoQLdaGhmrEgL+qrubh ooPqpdE2q14x8tB6/27fWohziH63Fe/+UciuKj7vVVwnQP4Re5oT1nPVf/SEnizT233t fcBerBsjXPtEdmiMmvcEzLaG9vjIeAmZip5zhaba0xFNdDbH10sz7B07eQW1Y9sMRe5f TLNiQ8s/box8LY1XxhIDiyJuBqD8DC88fdFq5TFEHqteG062uRItQnzlLgbK4a22nBk7 uXMA== X-Gm-Message-State: AOAM531hWPf9/35HmzhW8GsH5LY7m5ZtzSORtszfttPnyiralHYMKZ8b fBSoWDynhECd3pk2WOm4MErnMf8cBa/T5mqYGdCO4Q== X-Google-Smtp-Source: ABdhPJweQq+krXsUDsoeOuS4izGdW2bpWPGAcnA8SsKmxmctBiSz3y8JmTYbQnPZ+PkDcdOM5HQzhkzgI3dU7uno8zA= X-Received: by 2002:a25:2351:: with SMTP id j78mr30757910ybj.391.1624267221792; Mon, 21 Jun 2021 02:20:21 -0700 (PDT) MIME-Version: 1.0 References: <20210617095309.3542373-1-stapelberg+linux@google.com> In-Reply-To: From: Michael Stapelberg Date: Mon, 21 Jun 2021 11:20:10 +0200 Message-ID: Subject: Re: [PATCH] backing_dev_info: introduce min_bw/max_bw limits To: Miklos Szeredi Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm , linux-fsdevel@vger.kernel.org, Tejun Heo , Dennis Zhou , Jens Axboe , Roman Gushchin , Johannes Thumshirn , Jan Kara , Song Liu , David Sterba Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hey Miklos On Fri, 18 Jun 2021 at 16:42, Miklos Szeredi wrote: > > On Fri, 18 Jun 2021 at 10:31, Michael Stapelberg > wrote: > > > Maybe, but I don=E2=80=99t have the expertise, motivation or time to > > investigate this any further, let alone commit to get it done. > > During our previous discussion I got the impression that nobody else > > had any cycles for this either: > > https://lore.kernel.org/linux-fsdevel/CANnVG6n=3DySfe1gOr=3D0ituQidp56i= dGARDKHzP0hv=3DERedeMrMA@mail.gmail.com/ > > > > Have you had a look at the China LSF report at > > http://bardofschool.blogspot.com/2011/? > > The author of the heuristic has spent significant effort and time > > coming up with what we currently have in the kernel: > > > > """ > > Fengguang said he draw more than 10K performance graphs and read even > > more in the past year. > > """ > > > > This implies that making changes to the heuristic will not be a quick f= ix. > > Having a piece of kernel code sitting there that nobody is willing to > fix is certainly not a great situation to be in. Agreed. > > And introducing band aids is not going improve the above situation, > more likely it will prolong it even further. Sounds like =E2=80=9CPerfect is the enemy of good=E2=80=9D to me: you=E2=80= =99re looking for a perfect hypothetical solution, whereas we have a known-working low risk fix for a real problem. Could we find a solution where medium-/long-term, the code in question is improved, perhaps via a Summer Of Code project or similar community efforts, but until then, we apply the patch at hand? As I mentioned, I think adding min/max limits can be useful regardless of how the heuristic itself changes. If that turns out to be incorrect or undesired, we can still turn the knobs into a no-op, if removal isn=E2=80=99t an option. Thanks Best regards Michael