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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E731C4332F for ; Tue, 20 Dec 2022 22:55:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229448AbiLTWzr (ORCPT ); Tue, 20 Dec 2022 17:55:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229750AbiLTWzq (ORCPT ); Tue, 20 Dec 2022 17:55:46 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1A36810C3 for ; Tue, 20 Dec 2022 14:55:45 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 92CB6B81A40 for ; Tue, 20 Dec 2022 22:55:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31260C433D2; Tue, 20 Dec 2022 22:55:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1671576942; bh=9STm0HhHbUfuZ4BE7lXoLEHC3jdSnO12bfmTztliyYs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=NkHD+iJgRdCpFd7bRBGeH6d+icDac/DtFMd+8zLXLLKmm17qlVuCtOQF0PXMMjrZ/ 0sANpzi6fquUwicc59FdCeczz1yHPtEJvP0q+N9S+GqstrGQ/VkV1wIQ/YwzF5iKSD ydVIndwf1V26ZPRi48lLb5A4QfXCYzEd7lM+UqEWCX/RIVvr/Ewcc/pzOKucOl1Eed v7Dzv66a7UvzqZDNdhuMYB6laxO2XrHfoqKCzIYge/zonGGXEZ6unHWIxD9zIJwn6J Ere+zyO4aczNmrO363MuVq6xzBFvSvFWUUxCi/Kn7DY+9joTjO2tTl0Kry6zX4odx6 40iY4KvnHQqhw== Date: Tue, 20 Dec 2022 14:55:41 -0800 From: "Darrick J. Wong" To: "yangx.jy@fujitsu.com" Cc: xfs Subject: Re: Question about xfs/440 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Dec 16, 2022 at 01:02:18PM +0000, yangx.jy@fujitsu.com wrote: > Hi Darrick, > > As you know, the following steps comes from xfs/440. I have two > questions about these steps. > The first one: > Why repquota -u command shows "128" rather than "64" for fsgqa user > after cp --reflink command is completed? Quota resource usage are charged for each file, even for shared blocks. There's no easy way to amortize the cost of a shared block among its owners unless you can walk backwards from a piece of storage back to its owners, which is too much work to make it worth the effort. Hence reflinking a 64k file to another file creates 128k worth of usage. > The second one: > Why repquota -u command shows "1152" for fsgqa user after CoW(Copy on > Write) is completed? The space extents used to stage COW operations are separate space allocations, which means they're charged to the quota and hang around until writeback happens. In xfs/440, we set a cow extent size hint of 1mb, so we've actually staged 1mb of cow so that appending writes to /b will end up in contiguous space. That's why usage goes from 128 to 1152. --D > > How does the kernel process reflink and CoW? > How does the kernel calculate the number(e.g. 128，1152)? > > # mount -o usrquota,grpquota /dev/pmem1 /mnt/scratch/ > # touch /mnt/scratch/a /mnt/scratch/force_fsgqa > # chown fsgqa /mnt/scratch/a /mnt/scratch/force_fsgqa > # xfs_io -c "pwrite -S 0x58 0 64k" /mnt/scratch/a > # repquota -u /mnt/scratch/ > ... > Block limits File limits > User used soft hard grace used soft hard grace > ---------------------------------------------------------------------- > root -- 0 0 0 3 0 0 > fsgqa -- 64 0 0 2 0 0 > > # cp --reflink=always -p /mnt/scratch/a /mnt/scratch/b > # repquota -u /mnt/scratch/ > ... > Block limits File limits > User used soft hard grace used soft hard grace > ---------------------------------------------------------------------- > root -- 0 0 0 3 0 0 > fsgqa -- 128 0 0 3 0 0 > > # xfs_io -c "pwrite -S 0x59 0 64k" /mnt/scratch/a > # repquota -u /mnt/scratch/ > ... > Block limits File limits > User used soft hard grace used soft hard grace > ---------------------------------------------------------------------- > root -- 0 0 0 3 0 0 > fsgqa -- 1152 0 0 3 0 0 > > Best Regards, > Xiao Yang