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Tue, 06 Apr 2021 12:00:00 -0700 (PDT) Received: from dschatzberg-fedora-PC0Y6AEN.dhcp.thefacebook.com ([2620:10d:c091:480::1:438]) by smtp.gmail.com with ESMTPSA id d10sm16484412qko.70.2021.04.06.11.59.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Apr 2021 12:00:00 -0700 (PDT) Date: Tue, 6 Apr 2021 14:59:57 -0400 From: Dan Schatzberg To: Hillf Danton Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/3] loop: Use worker per cgroup instead of kworker Message-ID: References: <20210402191638.3249835-1-schatzberg.dan@gmail.com> <20210403020902.1384-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210403020902.1384-1-hdanton@sina.com> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 66ECAE000119 X-Stat-Signature: kiyuj8rdwr8bs8x7zh86w1ngkrc5c7do Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf13; identity=mailfrom; envelope-from=""; helo=mail-qk1-f176.google.com; client-ip=209.85.222.176 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617735599-858487 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Hillf, thanks for the review On Sat, Apr 03, 2021 at 10:09:02AM +0800, Hillf Danton wrote: > On Fri, 2 Apr 2021 12:16:32 Dan Schatzberg wrote: > > +queue_work: > > + if (worker) { > > + /* > > + * We need to remove from the idle list here while > > + * holding the lock so that the idle timer doesn't > > + * free the worker > > + */ > > + if (!list_empty(&worker->idle_list)) > > + list_del_init(&worker->idle_list); > > Nit, only queue work if the worker is inactive - otherwise it is taking > care of the cmd_list. By worker is inactive, you mean worker is on the idle_list? Yes, I think you're right that queue_work() is unnecessary in that case since each worker checks empty cmd_list then adds itself to idle_list under the lock. > > > + work = &worker->work; > > + cmd_list = &worker->cmd_list; > > + } else { > > + work = &lo->rootcg_work; > > + cmd_list = &lo->rootcg_cmd_list; > > + } > > + list_add_tail(&cmd->list_entry, cmd_list); > > + queue_work(lo->workqueue, work); > > + spin_unlock_irq(&lo->lo_work_lock); > > } > [...] > > + /* > > + * We only add to the idle list if there are no pending cmds > > + * *and* the worker will not run again which ensures that it > > + * is safe to free any worker on the idle list > > + */ > > + if (worker && !work_pending(&worker->work)) { > > The empty cmd_list is a good enough reason for worker to become idle. This is only true with the above change to avoid a gratuitous queue_work(), right? Otherwise we run the risk of freeing a worker concurrently with loop_process_work() being invoked.