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=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 5F778C4338F for ; Fri, 23 Jul 2021 02:41:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 447F260ED3 for ; Fri, 23 Jul 2021 02:41:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233485AbhGWCAv (ORCPT ); Thu, 22 Jul 2021 22:00:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:43744 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233238AbhGWCAu (ORCPT ); Thu, 22 Jul 2021 22:00:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 96A9960EBF; Fri, 23 Jul 2021 02:41:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627008084; bh=JSAe/f6FLauxnrmz5Uq68q6e5ZvuMKEjBqoyrMmhzpQ=; h=Subject:To:References:From:Date:In-Reply-To:From; b=aIX5knDUMaNsdXTyV8roJWrHI4dBY+/KrlZGPP8Dw3gytFDkhvvzT7tO4oETmLD+b /9n2C4kCWz7q6DHvbEm7SV42vDdGI/UnMUb9QmZ+fTNhWWJiuSoBKtivcQnAItn0C0 GfZaxiRm+HLQ7s6v/FjaoF0jf3e/AaZgIcxBbPdDJGq/O9lEowGHuHHmQVFfT6eYHm 7hbVBfyjZbF2it6vyptN+o7g9h4S+5bnwoEttBldLdn3fQkTyUnbNDjrZr1oDPtxI8 EoN3dniWaYjIDrS/C1aPbD5rY4NVW1Mb70ISbu1bZ1e+D6TNz3b2ZwaBWPZDdcjU63 g5ZcF/OSScsKw== Subject: Re: [f2fs-dev] [PATCH v3] f2fs: don't sleep while grabing nat_tree_lock To: Jaegeuk Kim , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net References: <20210722014149.525166-1-jaegeuk@kernel.org> From: Chao Yu Message-ID: <014f9855-3268-1d7e-98b6-0b8eb252bf39@kernel.org> Date: Fri, 23 Jul 2021 10:41:21 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/7/23 10:35, Jaegeuk Kim wrote: > This tries to fix priority inversion in the below condition resulting in > long checkpoint delay. > > f2fs_get_node_info() > - nat_tree_lock > -> sleep to grab journal_rwsem by contention > > checkpoint > - waiting for nat_tree_lock > > In order to let checkpoint go, let's release nat_tree_lock, if there's a > journal_rwsem contention. > > Signed-off-by: Daeho Jeong > Signed-off-by: Jaegeuk Kim > --- > Change log from v2: > - don't bother checkpoint > > fs/f2fs/node.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c > index 0be9e2d7120e..b26642daa3d2 100644 > --- a/fs/f2fs/node.c > +++ b/fs/f2fs/node.c > @@ -552,7 +552,7 @@ int f2fs_get_node_info(struct f2fs_sb_info *sbi, nid_t nid, > int i; > > ni->nid = nid; > - > +retry: > /* Check nat cache */ > down_read(&nm_i->nat_tree_lock); > e = __lookup_nat_cache(nm_i, nid); > @@ -564,10 +564,19 @@ int f2fs_get_node_info(struct f2fs_sb_info *sbi, nid_t nid, > return 0; > } > > - memset(&ne, 0, sizeof(struct f2fs_nat_entry)); > + /* > + * Check current segment summary by trying to grab journal_rwsem first. > + * This sem is on the critical path on the checkpoint requiring the above > + * nat_tree_lock. Therefore, we should retry, if we failed to grab here > + * while not bothering checkpoint. > + */ > + if (rwsem_is_locked(&sbi->cp_global_sem)) { You mean: if (!rwsem_is_locked()) ? IMO, once CP is processing, all readers who needs read nat will be blocked... Thanks, > + down_read(&curseg->journal_rwsem); > + } else if (!down_read_trylock(&curseg->journal_rwsem)) { > + up_read(&nm_i->nat_tree_lock); > + goto retry; > + } > > - /* Check current segment summary */ > - down_read(&curseg->journal_rwsem); > i = f2fs_lookup_journal_in_cursum(journal, NAT_JOURNAL, nid, 0); > if (i >= 0) { > ne = nat_in_journal(journal, i); >