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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 2D53EC4338F for ; Mon, 9 Aug 2021 18:26:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A73860F8F for ; Mon, 9 Aug 2021 18:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231830AbhHIS1E (ORCPT ); Mon, 9 Aug 2021 14:27:04 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:48098 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S234638AbhHIS1D (ORCPT ); Mon, 9 Aug 2021 14:27:03 -0400 Received: from cwcc.thunk.org (pool-72-74-133-215.bstnma.fios.verizon.net [72.74.133.215]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 179IQWrP022654 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 9 Aug 2021 14:26:33 -0400 Received: by cwcc.thunk.org (Postfix, from userid 15806) id 8F68915C3DD0; Mon, 9 Aug 2021 14:26:32 -0400 (EDT) Date: Mon, 9 Aug 2021 14:26:32 -0400 From: "Theodore Ts'o" To: ValdikSS Cc: linux-ext4@vger.kernel.org Subject: Re: ext4lazyinit reads HDD data on mount since 5.13 Message-ID: References: <015c7506-7f33-3967-772a-1285b0f1052f@valdikss.org.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Mon, Aug 09, 2021 at 10:43:08AM +0300, ValdikSS wrote: > On 09.08.2021 04:51, Theodore Ts'o wrote: > > It's a new feature which optimizes block allocations for very large > > file systems. The work being done by ext4lazyinit is to read the > > block allocation bitmaps so we can cache the buddy bitmaps and how > > fragmented (or not) various block groups are, which is used to > > optimize the block allocator. > > Thanks for the info. To revert old behavior, the filesystem should be > mounted with -o no_prefetch_block_bitmaps > > Is it safe to use this option with new optimizations? Should I expect only > less optimal filesystem speed and no other issues? It's not been tested, but it should be safe in terms that it shouldn't lead to any file system corruption or data loss. However, it may result in non-optional block placement that might cause more file or free-space fragmentation that might otherwise be the case. (This was true even before the latest optimizations, but it's more the case with the new optimizations.) Can you say something about why you want to disable to block allocation prefetch? How is it causing problems for you? Cheers, - Ted