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=-7.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 CD3FEC433DF for ; Tue, 25 Aug 2020 17:38:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A89FC2068E for ; Tue, 25 Aug 2020 17:38:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726119AbgHYRit (ORCPT ); Tue, 25 Aug 2020 13:38:49 -0400 Received: from mail-pf1-f195.google.com ([209.85.210.195]:34104 "EHLO mail-pf1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbgHYRir (ORCPT ); Tue, 25 Aug 2020 13:38:47 -0400 Received: by mail-pf1-f195.google.com with SMTP id m71so7918281pfd.1 for ; Tue, 25 Aug 2020 10:38:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Q+YopeIkFRKGljUOw9EJi+OWYEbgdLf5N6jXFJDCqtM=; b=SFgHLLBM0s0QpsKroTl4xDn4JgXZubbl9cdXwcmEQ0MjQAj7pw0Fo707Kf1zYqHvta 7ikXr1iwRRDMu66yw2y7CgRLCSMOewuadU6ZzlfW+EemQdtk7Gg4e+CFC7E+BStY5SL5 MMZ39w5LXFqjxuCdcOkwKkTQSjLj8IG1ocNNIYUvfRFGiUPZ6ck9S9u5znR3dnL1hIzB WT/hCYkxvy/TDx9aEV3zyp/U6MFp+Imo1lI+6HQtGQGviCR5SKxTjOmfan/cR4IAmnaZ abOi5SWiH662mf8FhHPVV9Ln3KHqTarVhUX0TiBQR5ab5wyMFKrBmdIMLF/HLSk2jeNH fEQA== X-Gm-Message-State: AOAM5313/aTPFhH6/RFdOPbnS0bfsHxoWnK13LuJHJtbZEIoNdh4ztwp wa04qx3OF6eVzQUoMwVZKAQ= X-Google-Smtp-Source: ABdhPJzkJAHG74gWjBtjtVpObp+kp9wrD8hna3apKpWDDk5qVaPcsN7cE4dIe74FlmAbew2/cffvwg== X-Received: by 2002:a17:902:9b8d:: with SMTP id y13mr6677036plp.90.1598377126510; Tue, 25 Aug 2020 10:38:46 -0700 (PDT) Received: from ?IPv6:2601:647:4802:9070:4c51:77cf:ef42:8603? ([2601:647:4802:9070:4c51:77cf:ef42:8603]) by smtp.gmail.com with ESMTPSA id t25sm15616864pfe.76.2020.08.25.10.38.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Aug 2020 10:38:45 -0700 (PDT) Subject: Re: [PATCH] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING To: Chao Leng , Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Lai Jiangshan , "Paul E . McKenney" , Josh Triplett , Bart Van Assche , Johannes Thumshirn , Christoph Hellwig References: <20200820030248.2809559-1-ming.lei@redhat.com> <856f6108-2227-67e8-e913-fdef296a2d26@grimberg.me> <20200822133954.GC3189453@T590> <619a8d4f-267f-5e21-09bd-16b45af69480@grimberg.me> <20200824104052.GA3210443@T590> <44160549-0273-b8e6-1599-d54ce84eb47f@grimberg.me> <20200825023212.GA3233087@T590> <399888c3-71e6-625e-3b0d-025ccbad4fd1@huawei.com> From: Sagi Grimberg Message-ID: <6cef7a24-f19c-a39a-abd8-2f0ea50fb7a2@grimberg.me> Date: Tue, 25 Aug 2020 10:38:43 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <399888c3-71e6-625e-3b0d-025ccbad4fd1@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org >>>> Good, but I'd also won't want to get this without making sure the async >>>> quiesce works well on large number of namespaces (the reason why this >>>> is proposed in the first place). Not sure who is planning to do that... >>> >>> That can be added when async quiesce is done. >> >> Chao, are you looking into that? I'd really hate to find out we have an >> issue there post conversion... > > Now we config CONFIG_TREE_SRCU, the size of TREE_SRCU is too big. I > really appreciate the work of Ming. > > I review the patch, I think the patch may work well now, but do extra > works for exception scenario. Percpu_ref is not disigned for > serialization which read low cost. If we replace SRCU with percpu_ref, > the benefit is save memory for blocking queue, the price is limit future > changes or do more extra works. > > I do not think replace SRCU with percpu_ref is a good idea, because it's > hard to predict how much we'll lose. Not sure I understand your point, can you clarify what is the poor design of percpu_ref and for which use-case?