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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 57758C43603 for ; Tue, 17 Dec 2019 18:44:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 28CC820716 for ; Tue, 17 Dec 2019 18:44:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576608278; bh=yMNL98MIHvH5NFnA0hq/yDU8AnnJQTx88CMou8Yyfk0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=N4W8+RfyW4ia3f2pjA2jCW64oxS55+RmZtmA2vCziOdpU9lEX66gXS3xLGCEdoejX UTgnCoohE/fUjRzG2A+OIuydvGxmcXHl2qGYtHyv+9yq0cuF2QzwSlQlEFM9kWZdva wzCXGVKHtnKkNZ0B2DaSh2a9Q4mJ6/cur1sM55Tw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727767AbfLQSoh (ORCPT ); Tue, 17 Dec 2019 13:44:37 -0500 Received: from mail-qk1-f193.google.com ([209.85.222.193]:40756 "EHLO mail-qk1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727577AbfLQSoh (ORCPT ); Tue, 17 Dec 2019 13:44:37 -0500 Received: by mail-qk1-f193.google.com with SMTP id c17so8327276qkg.7 for ; Tue, 17 Dec 2019 10:44:36 -0800 (PST) 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:user-agent; bh=em3ydnYiwFDAO9RTgcHEfhtwAEIdX3KXlxx4yRGRpJk=; b=sOKfI3HjKwTYUZ7JfIOxQ6OyigLL6afmW95WZRgDCf+Q4BJJhp40eX0lF9hQsMAnGn CNbc5NR7fPxIeQcRakv5XZt7bRHxArxrK1Kahkn/8KDYy6DjWZqxOlDiROcTkOsO+Uba wWU7Yi0YjsVN15aom6+llbkTWZwmYembtHXVq4QGil9I77FeCpKRY/ROLDwVJDVkh/WZ QdCiGvFb5UD5kNs8kA12Nk/hySFv16q5zZGDqQYbO0h3JymfaMIYD015FMGk7ltvKba4 HtsIId0Px52ZmCc5YkWkXOgUS/c6sokUMoDntdW3mRU2EcYT04cvW3gFfMOquCRiNcZw 8wbw== X-Gm-Message-State: APjAAAUaS6uq/Dbzx393z+2z5DuHc7sPOkZFDBZo27cFuZEkIxv+qgfH q3oW+e+P/tF9No+MidEYdsM= X-Google-Smtp-Source: APXvYqzI+hRnsk2fMPrUebro4r6zWiguvXpLkPhtos335G9uFLX6kZygS4gxBLPhSVaYFnN3ZZNK5w== X-Received: by 2002:a37:de16:: with SMTP id h22mr6636519qkj.400.1576608276319; Tue, 17 Dec 2019 10:44:36 -0800 (PST) Received: from dennisz-mbp ([2620:10d:c091:500::1246]) by smtp.gmail.com with ESMTPSA id o201sm7225355qka.17.2019.12.17.10.44.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Dec 2019 10:44:35 -0800 (PST) Date: Tue, 17 Dec 2019 13:44:33 -0500 From: Dennis Zhou To: David Sterba Cc: Dennis Zhou , David Sterba , Chris Mason , Josef Bacik , kernel-team@fb.com, linux-btrfs@vger.kernel.org Subject: Re: [PATCH v2 2/2] btrfs: fix compressed write bio attribution Message-ID: <20191217184433.GA2823@dennisz-mbp> References: <20191212181934.GA33645@dennisz-mbp.dhcp.thefacebook.com> <20191213122401.GV3929@suse.cz> <20191213222149.GA46346@dennisz-mbp.dhcp.thefacebook.com> <20191217150548.GF3929@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191217150548.GF3929@suse.cz> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Tue, Dec 17, 2019 at 04:05:48PM +0100, David Sterba wrote: > On Fri, Dec 13, 2019 at 02:21:49PM -0800, Dennis Zhou wrote: > > On Fri, Dec 13, 2019 at 01:24:01PM +0100, David Sterba wrote: > > > On Thu, Dec 12, 2019 at 10:19:34AM -0800, Dennis Zhou wrote: > > > > From a0569aebde08e31e994c92d0b70befb84f7f5563 Mon Sep 17 00:00:00 2001 > > > > From: Dennis Zhou > > > > Date: Wed, 11 Dec 2019 15:20:15 -0800 > > > > > > > > Bio attribution is handled at bio_set_dev() as once we have a device, we > > > > have a corresponding request_queue and then can derive the current css. > > > > In special cases, we want to attribute to bio to someone else. This can > > > > be done by calling bio_associate_blkg_from_css() or > > > > kthread_associate_blkcg() depending on the scenario. Btrfs does this for > > > > compressed writeback as they are handled by kworkers, so the latter can > > > > be done here. > > > > > > > > Commit 1a41802701ec ("btrfs: drop bio_set_dev where not needed") removes > > > > early bio_set_dev() calls prior to submit_stripe_bio(). This breaks the > > > > above assumption that we'll have a request_queue when we are doing > > > > association. To fix this, switch to using kthread_associate_blkcg(). > > > > > > Can be kthread_associate_blkcg used also for submit_extent_page that > > > calls bio_associate_blkg_from_css indirectly when initializing wbc? > > > > > > 2996 bio_set_dev(bio, bdev); > > > 2997 wbc_init_bio(wbc, bio); > > > 2998 wbc_account_cgroup_owner(wbc, page, page_size); > > > > > > wbc_init_bio: > > > > > > if (wbc) > > > bio_associate_blkg_from_css(); > > > > Correct me if I'm wrong, but I don't think submit_extent_page() is only > > called from kthread contexts. So, we wouldn't be able to rely on > > kthread_associate_blkcg(). > > Yeah, the kthread is not guaranteed here. > > > I can think about how to make wbc better for association in general, but > > it's a percpu decrement and increment so it shouldn't really be much in > > overhead. > > Performance is not my concern here, the addition of bios and blkcg > association is new and there were some integration bugs where I > independently removed early bdev association while the blkg relied on > that. I'm looking for ways to make it less error prone and the kthread > association looks exactly like that so I was curious if it's possible to > use it everywhere. If not, the bdev needs to be found from other > available data. Yeah. At the time, going through bio_set_dev() was a way to guarantee we weren't missing an association with a blk-cgroup. This simplified auditing and prevented newer use cases from missing it. However, I do agree it's quite error prone.. I'll put it on my list and see if I can come up with something better. Thanks, Dennis