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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 45C65C11F68 for ; Wed, 30 Jun 2021 14:50:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F7A761424 for ; Wed, 30 Jun 2021 14:50:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235215AbhF3Owd (ORCPT ); Wed, 30 Jun 2021 10:52:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235177AbhF3Owc (ORCPT ); Wed, 30 Jun 2021 10:52:32 -0400 Received: from mail-qv1-xf32.google.com (mail-qv1-xf32.google.com [IPv6:2607:f8b0:4864:20::f32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2055CC061756; Wed, 30 Jun 2021 07:50:03 -0700 (PDT) Received: by mail-qv1-xf32.google.com with SMTP id p7so1218037qvn.5; Wed, 30 Jun 2021 07:50:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7non7Ht3wU/Vgs0c/H0HW+wlwkdFp/0NZ1g7sAhRaEc=; b=gGD9BAtpYOeepZdTbE3KHgAiQMcPPfpnG9JJlnbUMfEhlC8BfSFmt8miSEvOuIEZiB 3rzRcjaUvadqxpFG1/UCWQxX3S4rZ592U9H9rz8afxfdqc1r2Rde8c8BEn9i7xgMhNDv JPyYE28nZZUx9+NLzRiuD3VmblJGAy13TwSeiDfi41Y1wHRqNK+gLcQjTZxfG2M1YsUZ 0c2kCQtqWyTPbUPzKbLyuJMbmCzox2eNsaFegX5bjW/wN/jIK4/VDB9Z58im/s+xDGmz cCYbg8XIqnEdiJwNjEYwVOBbY9TWqJad9qQ5AqQ/TxIfy00Mt1Ykar5zkLmd3VYYunt6 2M3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7non7Ht3wU/Vgs0c/H0HW+wlwkdFp/0NZ1g7sAhRaEc=; b=PDPMaTjq1k6GTeER9af4SASAxCKlnBWzj4eWr85gENLUVdWfEPb/76p1xLSBpApgxi hwnwadc+2ybQbM+RQzxyTvO8WQZyMOdEauz3cOoxH5ZejXmq2Ny4ev7oqCOLV7OXhGig cc4Qq4L+QlpoJ7EWHSMtrtvP4fmKVNir/IhAcqRKdN4TNDl77jM0SEIy1Z4u3ZsqW5E9 ueU2sn7+XFPtW0YImxYzusV6rOZijeJ0iE1vA+Peao7tvRyYWyVtSz02jmP3XjgVKbDa cLtFp1nSIF+1NjYWCfn1sWz1pez1r8RfxSqlzJqgdBjvx+5N9+CkrimHGwwUdCBSU2vW F/Dg== X-Gm-Message-State: AOAM532pvOHYbQWWMx5EqsDRJs0NrCkb2xGUs2VPNSxWhhmkGXF65/M1 4VWHC2j7tVN9P+2dLJD1Nc0= X-Google-Smtp-Source: ABdhPJzThHMaJANHAXxziTuH+SOn3cwvDIkQnU3dUtRtaQNsiFdcVi7NPiUTXYnhp8pT1LY+NU4BrQ== X-Received: by 2002:a05:6214:21ab:: with SMTP id t11mr21581134qvc.26.1625064602268; Wed, 30 Jun 2021 07:50:02 -0700 (PDT) Received: from dschatzberg-fedora-PC0Y6AEN ([2620:10d:c091:480::1:1008]) by smtp.gmail.com with ESMTPSA id g4sm5047069qtb.50.2021.06.30.07.50.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Jun 2021 07:50:01 -0700 (PDT) Date: Wed, 30 Jun 2021 10:49:58 -0400 From: Dan Schatzberg To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Andrew Morton , "open list:BLOCK LAYER" , open list , "open list:CONTROL GROUP (CGROUP)" , "open list:MEMORY MANAGEMENT" , Johannes Weiner , Jens Axboe Subject: Re: [PATCH 3/3] loop: Charge i/o to mem and blk cg Message-ID: References: <20210610173944.1203706-1-schatzberg.dan@gmail.com> <20210610173944.1203706-4-schatzberg.dan@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org > This is how I understand it: > > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -996,6 +996,7 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) > rb_insert_color(&worker->rb_node, &lo->worker_tree); > queue_work: > if (worker) { > + WARN_ON_ONCE(worker->blkcg_css != cmd->blkcg_css); Yes, this is correct. Though the check here seems a bit obvious to me - it must be correct because we assign worker above: if (cur_worker->blkcg_css == cmd->blkcg_css) { worker = cur_worker; break; or when we construct the worker: worker->blkcg_css = cmd->blkcg_css; I think this WARN_ON_ONCE check might be more interesting in loop_process_work which invokes loop_handle_cmd and actually uses cmd->blkcg_css. In any event, your understanding is correct here. > /* > * We need to remove from the idle list here while > * holding the lock so that the idle timer doesn't > @@ -2106,6 +2107,8 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, > cmd->memcg_css = NULL; > #ifdef CONFIG_BLK_CGROUP > if (rq->bio && rq->bio->bi_blkg) { > + /* reference to blkcg_css will be held by loop_worker (outlives > + * cmd) or it is the eternal root css */ Yes, this is correct. Feel free to add my Acked-by to such a patch