From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 2B8A73AE704; Mon, 21 Sep 2026 07:06:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789974380; cv=none; b=RoeBr5YiV4FF7R0m9skTmM4sKhYQavQcc0kPhSgY0EYiXKAkiSS4JF9V4WcBztC0hDolP2bwhca4tpjhUuau19Yh+mJeXfENIn6yawqVhFTcTYWmJ4KY9oiuKksOj7tLvb/Wjn5ngEEm8PjC+67dQ3759+wo7FF9aYLLWaHux9M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789974380; c=relaxed/simple; bh=TLj8sFutufMJiN3IAaR7TuLNFlZlrMDr3iGF+7yceIU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MNN1BFLzWclnjtXPZwkpad2SpbPCwOspcQSKfxYXE5j6whtLt3IUE58hGzJNtzA396+lH+FSai+aRwKCL3vJzUsMEhSAJJMY/A1eJ2Fj4JF+nWETHIJ8zH2nb6sIK8GbdIc8RJP2/npKL8KgOqHtTOYP4xDAmcl1xDH6ap73y4o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=EHQ++RBJ; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="EHQ++RBJ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=YruYuHsXYeu0Ni058efk89qmFUmonG8oukMq2C+cDTw=; b=EHQ++RBJi623ATzesXnFByagpi W5zLALfCy+QiWdW/z+K+duVjojGYX96UxIbgdlmdUT8+AsPwrLjleISvAF5tVQdPUK87xg2zOqZb9 sCHDyDEKDY53lYG3jMy2IYh2y1kGZFgxdnjbi4Mmf0LbZiT9mSygHFdulVL5dokE0gQJw8kLcddk8 Ogr+p44fOnmdCLAlaARb5Rr4/ze/TIe8gBWC/u1xaJLmMlemtg5ZX3q1JfFQobFNJKzgWR1QsUXmw W7KjmiuXX4msXorAOUNTXbQrXxNtZaO2+iV7+Jk7dwGf33IGIT9BVgH2sMR7ZXhGsgK0hPIeAE6re ljewyVmQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1x8Y6N-000000019eJ-3eau; Mon, 21 Sep 2026 07:06:11 +0000 Date: Mon, 21 Sep 2026 00:06:11 -0700 From: Christoph Hellwig To: Tejun Heo Cc: Tao Cui , Josef Bacik , josef@toxicopanda.com, Jens Axboe , Christoph Hellwig , 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: <9575357186118be214d6377dd80a21e8@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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.