From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B72484E7816; Mon, 21 Sep 2026 16:58:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790009886; cv=none; b=gD6s4bxE1KzlEBcHA0j/51hR45EWNzbTTP/TwPAW7sjdXSXgFBFJ4/E4vxbkLJwfvy/5ayQrI4/V4gcEp0juLuyFNGQFkWoa+DIQi5f/KkmDF781Aa48WQFWaKxSoZzWSG0pSG5HM8I/0MW7BTBsRKf3h422qJ+IP4xYE7eg3Rc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790009886; c=relaxed/simple; bh=afGAL0eN2aT15hmVo46YjA/ygEuBUt/5G7tioYm+Iuc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=iP3JoJwP7J3XPaZIlEy/HpOhq7EYLAh7KwZybsB1kROpUUAiV8HNRa2rY9asCDnQB4j1yKreBOKats8QzFagfCN0zl9kKtYlX2CCvVjbBPRh5d728AFGV9/rwtkSnhuOTuTBJeTgdZFOjjIrWG7JYzxi96f8V4so0YAWte1Smww= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ahwz/ahK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ahwz/ahK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B23C1F000FF; Mon, 21 Sep 2026 16:58:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790009884; bh=luSYIHzcViVqgBUn2upjQ2Gx8TpV50Xj9G/k+/YEy7I=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Ahwz/ahKbMoR1vjpIYwxO2R5Tlw43jvCFLWQPr5xat+RfHEBrAR/E6bqf1oxiNT5e DpgPAej2aayWMlhQkjuDFGaTzBi1CcgDyCrUwtmymZe9yYQcKO04ilquxWmi2eqrUn LrZZcTQXojHLVXlTokHgore2LROhMWWuY0Gfaeizz+cv7ia3kg6pKeUfK+6qDwGOKy f5OGUkoSbxyYBzWj82jaZoyHAXG0/lE0SZTSVQ8dGihk9B+eZ2bLjmJHnnLxBWoQAt ikN9eXxWFqcCyvS9pf7DfTRpryoAyKVfo9sXbxR0ada11kY+TOuFDHn01vda7jTIB/ FjxCelD53W9Zw== Date: Mon, 21 Sep 2026 06:58:03 -1000 From: Tejun Heo To: Christoph Hellwig Cc: Tao Cui , Josef Bacik , josef@toxicopanda.com, Jens Axboe , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, cuitao@kylinos.cn Subject: Re: [PATCH v2 1/4] blk-iocost: charge flushes as pageless random writes Message-ID: References: <20260916085304.1080271-1-cui.tao@linux.dev> <20260916085304.1080271-2-cui.tao@linux.dev> <9575357186118be214d6377dd80a21e8@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Sep 21, 2026 at 12:06:11AM -0700, Christoph Hellwig wrote: > On Sat, Sep 19, 2026 at 04:59:51AM -1000, Tejun Heo wrote: > > Hello, Tao. > > Pricing a flush as a random write, or as a page where that comes out to > > zero, is as arbitrary as pricing it at zero, > > No, it absolutely is not. For any flush that actually makes here it > is extremely expensive, and 0 is the wrongest possible value. Even > batching does not change that, as batching is not actually effective > in any normal file system workload. I see. I don't think the default value matters all that much given how crude a tool the default model is. We can set it to a page. I don't think we should impose it on existing users that are configuring custom models. Thanks. -- tejun