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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 9D77DC47088 for ; Wed, 26 May 2021 06:09:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82109613F4 for ; Wed, 26 May 2021 06:09:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232620AbhEZGLL (ORCPT ); Wed, 26 May 2021 02:11:11 -0400 Received: from mx2.suse.de ([195.135.220.15]:38734 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232657AbhEZGLJ (ORCPT ); Wed, 26 May 2021 02:11:09 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1622009376; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ySh2Hd2xbPPIm0hVylfe8g2a88Y2OpaZrYnAzKyUKqE=; b=ZdYOO33WPTl7gSQ804nc4Z8pOkobrpg8VhGw5uhH1xDKZCXfyq5jssorPs0bJxPjN09Cv+ KAoOvDKYZmj2HihpId29d5Q3kN2j535ZSY+9HKR0DT/tysisQxMXoqlt7Vu63ypCKrNEkP cB4fBRvCYItZfQ5ie8SFmjRB70kxAT8= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1622009376; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ySh2Hd2xbPPIm0hVylfe8g2a88Y2OpaZrYnAzKyUKqE=; b=gJljBv3QQ4Luvh8/DuLIMLyK7fNNFRI1XLRWnM1o53k/QmPvPlk4WiBlcaagL9h2oeNrLG rwiSQL55ty7mGsAg== Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 387C7B1AC; Wed, 26 May 2021 06:09:36 +0000 (UTC) Subject: Re: IO hang when cache do not have enough buckets on small SSD To: Jim Guo Cc: linux-bcache@vger.kernel.org References: <6c9fded6-30f8-b3cd-527b-0ca95fdca6ba@suse.de> From: Coly Li Message-ID: <3fb2d5bd-4e59-bad8-c3e7-1bcc58a4bea7@suse.de> Date: Wed, 26 May 2021 14:09:33 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-bcache@vger.kernel.org On 5/26/21 1:58 PM, Jim Guo wrote: >> What is the kernel version in your system? And where the kernel package >> is from? > I am using kernel version 4.19.142, I compile it from source code > downloaded from kernel.org. > >> Do you have a testing result on this idea? > Sorry, the testing environment is not owned by me and I did not keep > any testing result currently. I will test for this later in my own > testing environment. > OK. And I would suggest to start your work on upstream bcache code. Coly Li > Coly Li 于2021年5月17日周一 下午7:53写道： > >> >> On 5/17/21 11:54 AM, Jim Guo wrote: >>> Hello, Mr. Li. >>> Recently I was experiencing frequent io hang when testing with fio >>> with 4K random write. Fio iops dropped to 0 for about 20 seconds >>> every several minutes. >>> After some debugging, I discovered that it is the incremental gc that >>> cause this problem. >>> My cache disk is relatively small (375GiB with 4K block size and 512K >>> bucket size), backing hdds are 4 x 1 TiB. I cannot reproduce this on >>> another environment with bigger cache disk. >>> When running 4K random write fio bench, the buckets are consumed very >>> quickly and soon it has to invalidate some bucket (this happens quite >>> often). Since the cache disk is small, a lot of write io will soon >>> reach sectors_to_gc and trigger gc thread. Write io will also increase >>> search_inflight, which cause gc thread to sleep for 100ms. This will >>> cause gc procedure to execute for a long time, and invalidating bucket >>> for the write io will wait for the whole gc procedure. >>> After removing the 100ms sleep from the incremental gc patch, the io >>> never hang any more. >> >> What is the kernel version in your system? And where the kernel package >> is from? >> >> >>> I think for small ssd, sleeping for 100ms seems too long or maybe >>> write io should not trigger gc thread to sleep for 100ms? >>> Thank you very much. >>> >> >> Do you have a testing result on this idea? >> >> >> Thanks. >> >> Coly Li