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=-8.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 34F38C4338F for ; Thu, 29 Jul 2021 00:26:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0BACE60F5E for ; Thu, 29 Jul 2021 00:26:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232869AbhG2A01 (ORCPT ); Wed, 28 Jul 2021 20:26:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:42104 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232727AbhG2A01 (ORCPT ); Wed, 28 Jul 2021 20:26:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2465E60F59; Thu, 29 Jul 2021 00:26:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627518384; bh=uludeyf3+zGf2YO7V7UPfU6EFXH4cySzsy2ac4vsqZg=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=uc+72srOYR120uKGl7ZxsAJO2p0AMdqnnbO8mDXLYzC3n8ZaPT0qkoi/GV9IVP1l4 ZrAfzKwfU3hfAOrONYnqYPgHd/TnafG4/K9DAwHy3hO8MXHsRDFDB7pFClWg+3M/7Z BNTpulDwWjsDj9yXPrafyLei5OXfAXPV2yg+brRzltg7lyONSFwSlS0k9Rtt7h2sVj Ci/rZW1yQR/LSdLe1jRlUY4nsk9b3YXPAMeu9h94UPw15RdQjzOwEiGnYrpoCSOibp NzqUm9sTByxPYnLI1sSwefdqgKAfpdajK78xOVOUxykWCO6pPP+BHgnjYelPo75Qw8 ofqXEcTdeS8yA== Subject: Re: [PATCH 3/9] f2fs: rework write preallocations To: "Darrick J. Wong" Cc: Eric Biggers , Jaegeuk Kim , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, Satya Tangirala , Changheun Lee , Matthew Bobrowski References: <20210716143919.44373-1-ebiggers@kernel.org> <20210716143919.44373-4-ebiggers@kernel.org> <14782036-f6a5-878a-d21f-e7dd7008a285@kernel.org> <70f16fec-02f6-cb19-c407-856101cacc23@kernel.org> <70d9c954-d7f0-bbe2-f078-62273229342f@kernel.org> <20210727153335.GE559212@magnolia> From: Chao Yu Message-ID: Date: Thu, 29 Jul 2021 08:26:18 +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: <20210727153335.GE559212@magnolia> 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-xfs@vger.kernel.org On 2021/7/27 23:33, Darrick J. Wong wrote: > On Tue, Jul 27, 2021 at 04:30:16PM +0800, Chao Yu wrote: >> On 2021/7/27 15:38, Eric Biggers wrote: >>> That's somewhat helpful, but I've been doing some more investigation and now I'm >>> even more confused. How can f2fs support non-overwrite DIO writes at all >>> (meaning DIO writes in LFS mode as well as DIO writes to holes in non-LFS mode), >>> given that it has no support for unwritten extents? AFAICS, as-is users can >> >> I'm trying to pick up DAX support patch created by Qiuyang from huawei, and it >> looks it faces the same issue, so it tries to fix this by calling sb_issue_zeroout() >> in f2fs_map_blocks() before it returns. > > I really hope you don't, because zeroing the region before memcpy'ing it > is absurd. I don't know if f2fs can do that (xfs can't really) without > pinning resources during a potentially lengthy memcpy operation, but you > /could/ allocate the space in ->iomap_begin, attach some record of that > to iomap->private, and only commit the mapping update in ->iomap_end. Thanks for the suggestion, let me check this a little bit later, since now I just try to stabilize the codes... Thanks, > > --D > >>> easily leak uninitialized disk contents on f2fs by issuing a DIO write that >>> won't complete fully (or might not complete fully), then reading back the blocks >>> that got allocated but not written to. >>> >>> I think that f2fs will have to take the ext2 approach of not allowing >>> non-overwrite DIO writes at all... >> Yes, >> >> Another option is to enhance f2fs metadata's scalability which needs to update layout >> of dnode block or SSA block, after that we can record the status of unwritten data block >> there... it's a big change though... >> >> Thanks, >> >>> >>> - Eric >>>