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 1AE09560AB7; Tue, 22 Sep 2026 15:53:26 +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=1790092409; cv=none; b=S/VzluFDNGGbwr0yvHkDAyz7dCkOHX39Mp052fwzr42L6kAOc0KXu8keRrW/PPwGpDbc5iGhHWwBvL9CZ6vWWsFRrgVrM53XNmBtDpS1bt6i1WGisNKih6Dv0Ii9e7d1nCAXEHD+MQ1fnveqU1hy0GKqt53WJ450tPwueKeW4ss= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790092409; c=relaxed/simple; bh=wB0aNeEbuCMFPHnriodNEd2XAmMGFzXY19Re9KGMJSA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=oIhgeObNr0m+SOUh+tB4qQlm9AJo1kRREmDFpjNR+b6gPSKP8vPa6TskEWh9V0CARHNFUMxI26SjqqddD+ONE9zS0cMLdbqdkg55uy1siaf2x9Zwrxs8ENRgMKR6TYfNiVkcOWmN72610q9a8qJorZ2RFOsCl5ti16LdG3Qaz4M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L3RxkiWK; 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="L3RxkiWK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7903B1F000FF; Tue, 22 Sep 2026 15:53:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790092405; bh=cOoptst2ZoEH8nVl0gkhYSEwxHVp5gsU3BDINyMPqCg=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=L3RxkiWKuROFiw8J6LgOeWwybKXn/pxST7eaRsKu9zbMuQCmcYr65EAki0pMmLGsY QUnb1BPV09sM7D1bFA2bKnGLSB7AwqLsxKbt9PIO7p9uzvx/q+SK+SeHtm644Yiuxg 17lcVpXlyKlVCcMpVaqNBkaTnOkeDJzXqYDnw2/YhohjTtAzpZSHD13XMfpZqfCRBL wWoxESvTFgzXA6rqIQ4ltkXf+AN7zzarNPQYkokHpPwaDb9gdVV1HigU7KlMvwRm+b Dt+OkORRzZ3i/hIcAfUad0sq3sBkC72jD6fvb3nVn3XNeYPurIstKX/lZ8Nsev9lVu tq+HaVv6ccheQ== Date: Tue, 22 Sep 2026 05:53:24 -1000 From: Tejun Heo To: Tao Cui Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, yukuai@fygo.io, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, cuitao@kylinos.cn Subject: Re: [RFC PATCH 1/1] block: charge passthrough requests to the submitter's cgroup Message-ID: References: <20260921070647.1928289-1-cui.tao@linux.dev> <20260921070647.1928289-2-cui.tao@linux.dev> 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: Hello, On Tue, Sep 22, 2026 at 04:09:57PM +0800, Tao Cui wrote: > I don't have a specific passthrough workload that triggered this in > production. I ran into it while testing blk-iocost accounting coverage. > > The relevant concern here is cgroup IO isolation. The expectation of > blkcg IO control is that the IO consumed by a cgroup is reflected in its > accounting and subject to blkcg IO policies. Today that is true for IO > going through submit_bio(), but not for passthrough requests. > > The concrete observation was that the same cgroup issuing equivalent > writes through two paths gets different results: normal bio IO is > accounted in io.stat and subject to blkcg IO policies, while SG_IO > writes consume device bandwidth without accounting or blkcg IO control. > > So the motivation is not a particular SG_IO application, but whether > passthrough IO should be considered part of the IO usage controlled by > blkcg. > > I don't know yet whether the right answer is always-on behavior or an > opt-in mechanism. The RFC was mainly to discuss whether passthrough > paths should be covered by blkcg accounting/enforcement at all. SG_IO requires CAP_RAW_IO, so any kind of isolation isn't gonna work out that well. This is an imaginary use case. Please stop until it become an actual one. Thanks. -- tejun